View source for Heart

{{Short description|Organ found in humans and other animals}}
{{About|the internal organ|other uses|Heart (disambiguation)}}
{{Redirect|Cardiac|the computer programming tool|CARDIAC|the comics character|Cardiac (character)}}
{{good article}}
{{pp-semi-blp|small=yes}}
{{Use dmy dates|date=November 2020}}
{{Infobox anatomy
| Name = Heart
| Latin = cor
| Greek = καρδία (kardía)
| Width = 
| Image2 = [[File:Heart anterior exterior view.png|150px]]
| Caption2 = An illustration of the anterior view of the human heart
| Precursor =
| System = [[Circulatory system|Circulatory]]
| Artery = [[Aorta]],{{efn|From the heart to the body}} [[pulmonary trunk]] and right and left [[pulmonary artery|pulmonary arteries]],{{efn|Arteries that contain deoxygenated blood, from the heart to the lungs}} [[right coronary artery]], [[left main coronary artery]]{{efn|Supplying blood to the heart itself}}
| Vein = [[Superior vena cava]], [[inferior vena cava]],{{efn|From the body to the heart}} right and left [[pulmonary vein]]s,{{efn|Veins containing oxygenated blood from the lungs to the heart}} [[great cardiac vein]], [[middle cardiac vein]], [[small cardiac vein]], [[anterior cardiac veins]]{{efn|Veins that drain blood from the cardiac tissue itself}}
| Nerve = [[Accelerans nerve]], [[vagus nerve]]
| Lymph =
}}

<!-- Introduction -->
The '''heart''' is a muscular [[Organ (biology)|organ]] found in [[human]]s and other [[animal]]s. This organ pumps [[blood]] through the [[blood vessel]]s.<ref>{{Citation |last=Moran |first=Michael E. |title=Gray's Anatomy of Stones: Henry Vandyke Carter |date=2013-08-26 |work=Urolithiasis A Comprehensive History |pages=131–144 |place=New York, NY |publisher=[[Springer New York]] |doi=10.1007/978-1-4614-8196-6_15 |isbn=978-1-4614-8195-9}}</ref> The heart and blood vessels together make the [[circulatory system]].<ref name="tabers">{{cite book |author1=Taber, Clarence Wilbur |author2=Venes, Donald |title=[[Taber's Cyclopedic Medical Dictionary]] |publisher=[[F. A. Davis Company|F.A. Davis Co.]] |year=2009 |pages=1018–1023 |isbn=978-0-8036-1559-5 }}</ref> The pumped blood carries [[oxygen]] and [[nutrient]]s to the tissue, while carrying [[metabolic waste]] such as [[carbon dioxide]] to the [[lung]]s.{{sfn|Guyton & Hall|2011|p=157}} In [[human]]s, the heart is approximately the size of a closed [[fist]] and is located between the lungs, in the middle compartment of the [[thorax|chest]], called the [[mediastinum]].<ref name="Moore's 6">{{cite book|author1=Moore, Keith L. |author2=Dalley, Arthur F. |author3=Agur, Anne M.R. |title=Clinically Oriented Anatomy|publisher=[[Wolters_Kluwer#Operations|Wolters Kluwer Health]]/[[Lippincott Williams & Wilkins]]|isbn=978-1-60547-652-0|pages=127–173|chapter=1|year=2009 }}</ref>

<!--Structure-->
In humans, the heart is divided into four chambers: upper left and right [[Atrium (heart)|atria]] and lower left and right [[Ventricle (heart)|ventricles]].<ref name="StarrEvers2009">{{cite book|author1=Starr, Cecie|author2=Evers, Christine|author3=Starr, Lisa|title=Biology: Today and Tomorrow With Physiology|url=https://books.google.com/books?id=dxC27ndpwe8C&pg=PA422|year=2009|publisher=Cengage Learning|isbn=978-0-495-56157-6|page=422|url-status=live|archive-url=https://web.archive.org/web/20160502095349/https://books.google.com/books?id=dxC27ndpwe8C&pg=PA422|archive-date=2 May 2016}}</ref><ref name=K2008>{{cite book|last1=Reed|first1=C. Roebuck|last2=Brainerd|first2=Lee Wherry|last3=Lee|first3=Rodney|author4=Kaplan, Inc.|title=CSET: California Subject Examinations for Teachers|date=2008|publisher=Kaplan Pub.|location=New York|isbn=978-1-4195-5281-6|page=154|edition=3rd|url=https://books.google.com/books?id=1jjMzgEACAAJ|url-status=live|archive-url=https://web.archive.org/web/20160504211756/https://books.google.com/books?id=hP7n4Rki02EC&pg=PA154|archive-date=4 May 2016}}</ref> Commonly, the right atrium and ventricle are referred together as the [[right heart]] and their left counterparts as the [[left heart]].{{sfn|Gray's Anatomy|2008|p=960}} In a healthy heart, blood flows one way through the heart due to [[heart valve]]s, which prevent [[cardiac regurgitation|backflow]].<ref name="Moore's 6"/> The heart is enclosed in a protective sac, the [[pericardium]], which also contains a small amount of [[pericardial fluid|fluid]]. The wall of the heart is made up of three layers: [[epicardium]], [[myocardium]], and [[endocardium]].<ref name="CNX2014">{{cite book|last1=Betts|first1=J. Gordon|title=Anatomy & physiology|date=2013|isbn=978-1-938168-13-0|url=http://cnx.org/content/m46676/latest/?collection=col11496/latest|access-date=11 August 2014|pages=787–846|publisher=OpenStax College, Rice University |archive-date=27 February 2021|archive-url=https://web.archive.org/web/20210227144954/https://openstax.org/books/anatomy-and-physiology/pages/19-1-heart-anatomy|url-status=live}}</ref>  

<!--Function/Physiology-->
The heart pumps blood with a [[Heart rate|rhythm]] determined by a group of [[pacemaker cells]] in the [[sinoatrial node]]. These generate an electric current that causes the heart to contract, traveling through the [[atrioventricular node]] and along the [[conduction system of the heart]]. In humans, deoxygenated blood enters the heart through the right atrium from the [[superior vena cava|superior]] and [[inferior vena cava|inferior venae cavae]] and passes to the right ventricle. From here, it is pumped into [[pulmonary circulation]] to the [[lung]]s, where it receives oxygen and gives off carbon dioxide. Oxygenated blood then returns to the left atrium, passes through the left ventricle and is pumped out through the [[aorta]] into [[systemic circulation]], traveling through [[arteries]], [[arteriole]]s, and [[capillaries]]—where [[nutrient]]s and other substances are exchanged between blood vessels and cells, losing oxygen and gaining carbon dioxide—before being returned to the heart through [[venule]]s and [[vein]]s.{{sfn|Guyton & Hall|2011|pp=101, 157–158, 180}} The adult heart beats at a [[Resting heart rate|resting rate]] close to 72 beats per minute.{{sfn|Guyton & Hall|2011|pp=105–107}} [[Physical exercise|Exercise]] temporarily increases the rate, but lowers it in the long term, and is good for heart health.{{sfn|Guyton & Hall|2011|pp=1039–1041}}

<!--Clinical significance-->
[[Cardiovascular disease]]s were the most common cause of death globally as of 2008, accounting for 30% of all human deaths.<ref name="WHO CVD 2013"/><ref name="Harrisons">{{cite book|last1=Longo|first1=Dan|last2=Fauci|first2=Anthony|last3=Kasper|first3=Dennis|last4=Hauser|first4=Stephen|last5=Jameson|first5=J.|last6=Loscalzo|first6=Joseph|title=Harrison's Principles of Internal Medicine|year=2011|publisher=McGraw-Hill Professional|isbn=978-0-07-174889-6|page=1811|edition=18th}}</ref> Of these more than three-quarters are a result of [[coronary artery disease]] and [[stroke]].<ref name="WHO CVD 2013">{{cite web|title=Cardiovascular diseases (CVDs) Fact sheet N°317 March 2013|url=https://www.who.int/mediacentre/factsheets/fs317/en/|website=WHO|publisher=World Health Organization|access-date=20 September 2014|url-status=live|archive-url=https://web.archive.org/web/20140919020049/http://www.who.int/mediacentre/factsheets/fs317/en/|archive-date=19 September 2014}}</ref> Risk factors include: [[smoking]], being [[overweight]], little exercise, [[high cholesterol]], [[high blood pressure]], and poorly controlled [[diabetes]], among others.<ref>{{cite journal|last1=Graham|first1=I|last2=Atar|first2=D|last3=Borch-Johnsen|first3=K|last4=Boysen|first4=G|last5=Burell|first5=G|last6=Cifkova|first6=R|last7=Dallongeville|first7=J|last8=De Backer|first8=G|last9=Ebrahim|first9=S|last10=Gjelsvik|first10=B|last11=Herrmann-Lingen|first11=C|last12=Hoes|first12=A|last13=Humphries|first13=S|last14=Knapton|first14=M|last15=Perk|first15=J|last16=Priori|first16=SG|last17=Pyorala|first17=K|last18=Reiner|first18=Z|last19=Ruilope|first19=L|last20=Sans-Menendez|first20=S|last21=Scholte op Reimer|first21=W|last22=Weissberg|first22=P|last23=Wood|first23=D|last24=Yarnell|first24=J|last25=Zamorano|first25=JL|last26=Walma|first26=E|last27=Fitzgerald|first27=T|last28=Cooney|first28=MT|last29=Dudina|first29=A|last30=European Society of Cardiology (ESC) Committee for Practice Guidelines|first30=(CPG)|title=European guidelines on cardiovascular disease prevention in clinical practice: executive summary: Fourth Joint Task Force of the European Society of Cardiology and Other Societies on Cardiovascular Disease Prevention in Clinical Practice (Constituted by representatives of nine societies and by invited experts)|journal=European Heart Journal|date=Oct 2007|volume=28|issue=19|pages=2375–2414|pmid=17726041|doi=10.1093/eurheartj/ehm316|url=https://pure.qub.ac.uk/ws/files/498032/European%20guidelines%20on%20cardiovascular%20disease%20prevention%20in%20clinical%20practice%20-%20executive%20summary%20-%20Eur%20Heart%20J%202007%20-%20Yarnell%20JW%20(EACPR).pdf|doi-access=free|access-date=21 October 2019|archive-date=27 April 2019|archive-url=https://web.archive.org/web/20190427100116/https://pure.qub.ac.uk/ws/files/498032/European%20guidelines%20on%20cardiovascular%20disease%20prevention%20in%20clinical%20practice%20-%20executive%20summary%20-%20Eur%20Heart%20J%202007%20-%20Yarnell%20JW%20(EACPR).pdf|url-status=live}}</ref> Cardiovascular diseases do not frequently have symptoms but may cause [[chest pain]] or [[shortness of breath]]. Diagnosis of heart disease is often done by the taking of a [[medical history]], [[auscultation|listening]] to the [[heart-sound]]s with a [[stethoscope]], as well as with [[electrocardiogram|ECG]], and [[echocardiogram]] which uses [[ultrasound]].<ref name="Moore's 6"/> Specialists who focus on diseases of the heart are called [[cardiologists]], although many specialties of medicine may be involved in treatment.<ref name="Harrisons"/><!--Page 1819-->
{{listen
| filename = Emily's heartbeat.wav
| title = A teenager's heartbeat
| description = Sounds of a healthy 16-year-old female's heart beating normally, as heard with a [[stethoscope]].
| format = [[wav]]
}}
{{TOC limit}}

==Structure==
[[File:Humhrt2.jpg|thumbnail|200px|right|Human heart during an [[autopsy]]]]
[[File:CG Heart.gif|alt=Computer generated animation of a beating human heart|thumb|Computer-generated animation of a beating human heart]]
[[File:MC1 Cardiology 1.webm|thumb|Cardiology video]]
{{See also|Anatomy of the human heart}}

===Location and shape===
[[File:Real-time MRI - Thorax.ogv|thumb|[[Real-time MRI]] of the human heart]]
[[File:Heart near.png|thumb|left|upright|The human heart is in the middle of the [[thorax]], with its apex pointing to the left.<ref>{{cite web |url=http://www.bartleby.com/107/284.html |title=Gray's Anatomy of the Human Body – 6. Surface Markings of the Thorax |publisher=Bartleby.com |access-date=2010-10-18 |url-status=live |archive-url=https://web.archive.org/web/20101120145802/http://bartleby.com/107/284.html |archive-date=20 November 2010}}</ref>]]

The human heart is situated in the [[mediastinum]], at the level of [[thoracic vertebrae]] [[Fifth thoracic vertebra|T5]]–[[Eighth thoracic vertebra|T8]]. A double-membraned sac called the [[pericardium]] surrounds the heart and attaches to the mediastinum.<ref>{{cite book|last1=Dorland's|title=Dorland's Illustrated Medical Dictionary|date=2012|publisher=Elsevier|isbn=978-1-4160-6257-8|page=1461|edition=32nd}}</ref> The back surface of the heart lies near the [[vertebral column]], and the front surface, known as the sternocostal surface, sits behind the [[sternum]] and [[costal cartilage|rib cartilages]].<ref name="CNX2014"/> The upper part of the heart is the attachment point for several large blood vessels—the [[venae cavae]], [[aorta]] and [[pulmonary trunk]]. The upper part of the heart is located at the level of the third costal cartilage.<ref name="CNX2014"/> The lower tip of the heart, the '''apex''', lies to the left of the sternum (8 to 9&nbsp;cm from the [[midsternal line]]) between the junction of the fourth and fifth ribs near their [[articulation (anatomy)|articulation]] with the costal cartilages.<ref name="CNX2014"/>

The largest part of the heart is usually slightly offset to the left side of the chest ([[levocardia]]). In a rare congenital disorder ([[dextrocardia]]) the heart is offset to the right side and is felt to be on the left because the [[left heart]] is stronger and larger, since it pumps to all body parts. Because the heart is between the [[human lung|lungs]], the left lung is smaller than the right lung and has a cardiac notch in its border to accommodate the heart.<ref name="CNX2014"/>
The heart is cone-shaped, with its '''base''' positioned upwards and tapering down to the apex.<ref name="CNX2014"/> An adult heart has a mass of 250–350 grams (9–12&nbsp;oz).<ref>{{cite web|last1=Bianco|first1=Carl|title=How Your Heart Works|url=http://health.howstuffworks.com/human-body/systems/circulatory/heart1.htm|website=HowStuffWorks|access-date=14 August 2016|archive-url=https://web.archive.org/web/20160729035858/http://health.howstuffworks.com/human-body/systems/circulatory/heart1.htm|archive-date=29 July 2016|date=April 2000}}</ref> The heart is often described as the size of a fist: 12&nbsp;cm (5&nbsp;in) in length, 8&nbsp;cm (3.5&nbsp;in) wide, and 6&nbsp;cm (2.5&nbsp;in) in thickness,<ref name="CNX2014"/> although this description is disputed, as the heart is likely to be slightly larger.<ref>{{cite journal |last1=Ampanozi |first1=Garyfalia |last2=Krinke |first2=Eileen |last3=Laberke |first3=Patrick |last4=Schweitzer |first4=Wolf |last5=Thali |first5=Michael J. |last6=Ebert |first6=Lars C. |title=Comparing fist size to heart size is not a viable technique to assess cardiomegaly |journal=Cardiovascular Pathology|date=7 May 2018 |volume=36 |pages=1–5 |doi=10.1016/j.carpath.2018.04.009 |pmid=29859507 |s2cid=44086023 |issn=1879-1336}}</ref> Well-trained [[athlete]]s can have much larger hearts due to the effects of exercise on the heart muscle, similar to the response of skeletal muscle.<ref name="CNX2014"/>

===Chambers===
[[File:Heart diseccion.jpg|thumb|Heart being dissected showing right and left ventricles, from above]]
The heart has four chambers, two upper [[atrium (heart)|atria]], the receiving chambers, and two lower [[ventricle (heart)|ventricles]], the discharging chambers. The atria open into the ventricles via the [[atrioventricular valve]]s, present in the [[atrioventricular septum]]. This distinction is visible also on the surface of the heart as the [[coronary sulcus]].{{sfn|Gray's Anatomy|2008|pp=960–962}} There is an ear-shaped structure in the upper right atrium called the [[Atrium (heart)#Structure|right atrial appendage]], or auricle, and another in the upper left atrium, the [[Atrium (heart)#Structure|left atrial appendage]].{{sfn|Gray's Anatomy|2008|pp=964–967}} The right atrium and the right ventricle together are sometimes referred to as the [[right heart]]. Similarly, the left atrium and the left ventricle together are sometimes referred to as the [[left heart]].{{sfn|Gray's Anatomy|2008|p=960}} The ventricles are separated from each other by the [[interventricular septum]], visible on the surface of the heart as the [[anterior longitudinal sulcus]] and the [[posterior interventricular sulcus]].{{sfn|Gray's Anatomy|2008|pp=960–962}}

The [[dense connective tissue|fibrous]] [[cardiac skeleton]] gives structure to the heart. It forms the atrioventricular septum, which separates the atria from the ventricles, and the fibrous rings, which serve as bases for the four [[heart valve]]s.<ref>{{cite book|last1=Pocock|first1=Gillian|title=Human Physiology|date=2006|publisher=Oxford University Press|isbn=978-0-19-856878-0|page=264}}</ref> The cardiac skeleton also provides an important boundary in the heart's electrical conduction system since collagen cannot conduct [[electricity]]. The interatrial septum separates the atria, and the interventricular septum separates the ventricles.<ref name="CNX2014"/> The interventricular septum is much thicker than the interatrial septum since the ventricles need to generate greater pressure when they contract.<ref name="CNX2014"/>

====Valves====
{{Main|Heart valves}}
{{multiple image
| align = right
| direction = horizontal
| image1 = 2011 Heart Valves.jpg
| width1 = 230
| caption1 = With the atria and major vessels removed, all four valves are clearly visible.<ref name="CNX2014"/>
| image2 = Diagram_of_the_human_heart_(cropped).svg
| width2 = 184
| caption2 = The heart, showing valves, arteries and veins. The white arrows show the normal direction of blood flow.
}}

[[File:2010 Chordae Tendinae Papillary Muscles.jpg|thumb|Frontal section showing [[papillary muscle]]s attached to the [[tricuspid valve]] on the right and to the [[mitral valve]] on the left via [[chordae tendineae]].<ref name="CNX2014"/>]]
The heart has four valves, which separate its chambers. One valve lies between each atrium and ventricle, and one valve rests at the exit of each ventricle.<ref name=CNX2014/>

The valves between the atria and ventricles are called the atrioventricular valves. Between the right atrium and the right ventricle is the [[tricuspid valve]]. The tricuspid valve has three cusps,{{sfn|Gray's Anatomy|2008|pp=966–967}} which connect to [[chordae tendinae]] and three [[papillary muscle]]s named the anterior, posterior, and septal muscles, after their relative positions.{{sfn|Gray's Anatomy|2008|pp=966–967}} The [[mitral valve]] lies between the left atrium and left ventricle. It is also known as the bicuspid valve due to its having two cusps, an anterior and a posterior cusp. These cusps are also attached via chordae tendinae to two papillary muscles projecting from the ventricular wall.{{sfn|Gray's Anatomy|2008|p=970}}

The papillary muscles extend from the walls of the heart to valves by cartilaginous connections called chordae tendinae. These muscles prevent the valves from falling too far back when they close.<ref>{{cite web|author1=University of Minnesota|title=Papillary Muscles|url=http://www.vhlab.umn.edu/atlas/left-ventricle/papillary-muscles/index.shtml|website=Atlas of Human Cardiac Anatomy|access-date=7 March 2016|url-status=live|archive-url=https://web.archive.org/web/20160317203756/http://www.vhlab.umn.edu/atlas/left-ventricle/papillary-muscles/index.shtml|archive-date=17 March 2016}}</ref> During the relaxation phase of the cardiac cycle, the papillary muscles are also relaxed and the tension on the chordae tendineae is slight. As the heart chambers contract, so do the papillary muscles. This creates tension on the chordae tendineae, helping to hold the cusps of the atrioventricular valves in place and preventing them from being blown back into the atria.<ref name="CNX2014"/>{{efn|Note the muscles do '''not''' cause the valves to open. The pressure difference between the blood in the atria and the ventricles does this.}}{{sfn|Gray's Anatomy|2008|pp=966–967}}

Two additional semilunar valves sit at the exit of each of the ventricles. The [[pulmonary valve]] is located at the base of the [[pulmonary artery]]. This has three cusps which are not attached to any papillary muscles. When the ventricle relaxes blood flows back into the ventricle from the artery and this flow of blood fills the pocket-like valve, pressing against the cusps which close to seal the valve. The semilunar [[aortic valve]] is at the base of the [[aorta]] and also is not attached to papillary muscles. This too has three cusps which close with the pressure of the blood flowing back from the aorta.<ref name="CNX2014"/>

====Right heart====
{{anchor|Right heart}}
The right heart consists of two chambers, the right atrium and the right ventricle, separated by a valve, the [[tricuspid valve]].<ref name="CNX2014"/>

The right atrium receives blood almost continuously from the body's two major [[vein]]s, the [[Superior vena cava|superior]] and [[Inferior vena cava|inferior]] [[Vena cava|venae cavae]]. A small amount of blood from the coronary circulation also drains into the right atrium via the [[coronary sinus]], which is immediately above and to the middle of the opening of the inferior vena cava.<ref name="CNX2014"/> In the wall of the right atrium is an oval-shaped depression known as the [[fossa ovalis (heart)|fossa ovalis]], which is a remnant of an opening in the fetal heart known as the [[Foramen ovale (heart)|foramen ovale]].<ref name="CNX2014"/> Most of the internal surface of the right atrium is smooth, the depression of the fossa ovalis is medial, and the anterior surface has prominent ridges of [[pectinate muscle]]s, which are also present in the [[right atrial appendage]].<ref name="CNX2014"/>

The right atrium is connected to the right ventricle by the tricuspid valve.<ref name="CNX2014"/> The walls of the right ventricle are lined with [[trabeculae carneae]], ridges of cardiac muscle covered by endocardium. In addition to these muscular ridges, a band of cardiac muscle, also covered by endocardium, known as the [[moderator band]] reinforces the thin walls of the right ventricle and plays a crucial role in cardiac conduction. It arises from the lower part of the interventricular septum and crosses the interior space of the right ventricle to connect with the inferior papillary muscle.<ref name="CNX2014"/> The right ventricle tapers into the [[pulmonary trunk]], into which it ejects blood when contracting. The pulmonary trunk branches into the left and right pulmonary arteries that carry the blood to each lung. The pulmonary valve lies between the right heart and the pulmonary trunk.<ref name="CNX2014"/>

====Left heart====
{{anchor|left heart}}
The left heart has two chambers: the left atrium and the left ventricle, separated by the [[mitral valve]].<ref name="CNX2014"/>

The left atrium receives oxygenated blood back from the lungs via one of the four [[pulmonary vein]]s. The left atrium has an outpouching called the [[left atrial appendage]]. Like the right atrium, the left atrium is lined by [[pectinate muscles]].<ref>{{Cite web|url=http://medical-dictionary.thefreedictionary.com/pectinate+muscle|title=pectinate muscle|publisher=The Free Dictionary|access-date=2016-07-31|archive-date=23 August 2018|archive-url=https://web.archive.org/web/20180823131849/https://medical-dictionary.thefreedictionary.com/pectinate+muscle|url-status=live}}</ref> The left atrium is connected to the left ventricle by the mitral valve.<ref name="CNX2014"/>

The left ventricle is much thicker as compared with the right, due to the greater force needed to pump blood to the entire body. Like the right ventricle, the left also has [[trabeculae carneae]], but there is no [[moderator band]]. The left ventricle pumps blood to the body through the aortic valve and into the aorta. Two small openings above the aortic valve carry blood to the [[heart muscle]]; the [[left coronary artery]] is above the left cusp of the valve, and the [[right coronary artery]] is above the right cusp.<ref name="CNX2014"/>

===Wall===
{{Further|Cardiac muscle}}
[[File:2004 Heart Wall.jpg|thumb|Layers of the heart wall, including visceral and parietal pericardium]]

The heart wall is made up of three layers: the inner [[endocardium]], middle [[myocardium]] and outer [[epicardium]]. These are surrounded by a double-membraned sac called the pericardium.

The innermost layer of the heart is called the endocardium. It is made up of a lining of [[simple squamous epithelium]] and covers heart chambers and valves. It is continuous with the [[endothelium]] of the veins and arteries of the heart, and is joined to the myocardium with a thin layer of connective tissue.<ref name="CNX2014"/> The endocardium, by secreting [[endothelins]], may also play a role in regulating the contraction of the myocardium.<ref name="CNX2014"/>

[[File:2006 Heart Musculature.jpg|200px|thumbnail|The swirling pattern of myocardium helps the heart pump effectively]]The middle layer of the heart wall is the myocardium, which is the [[cardiac muscle]]—a layer of involuntary [[striated muscle tissue]] surrounded by a framework of [[collagen]]. The cardiac muscle pattern is elegant and complex, as the muscle cells swirl and spiral around the chambers of the heart, with the outer muscles forming a figure 8 pattern around the atria and around the bases of the great vessels and the inner muscles, forming a figure 8 around the two ventricles and proceeding toward the apex. This complex swirling pattern allows the heart to pump blood more effectively.<ref name="CNX2014"/>

There are two types of cells in cardiac muscle: [[cardiomyocyte|muscle cells]] which have the ability to contract easily, and [[cardiac pacemaker|pacemaker cells]] of the conducting system. The muscle cells make up the bulk (99%) of cells in the atria and ventricles. These contractile cells are connected by [[intercalated disc]]s which allow a rapid response to impulses of [[cardiac action potential|action potential]] from the pacemaker cells. The intercalated discs allow the cells to act as a [[syncytium]] and enable the contractions that pump blood through the heart and into the [[great arteries|major arteries]].<ref name="CNX2014"/> The pacemaker cells make up 1% of cells and form the conduction system of the heart. They are generally much smaller than the contractile cells and have few [[myofibril]]s which gives them limited contractibility. Their function is similar in many respects to [[neuron]]s.<ref name="CNX2014"/> Cardiac muscle tissue has [[autorhythmicity]], the unique ability to initiate a cardiac action potential at a fixed rate—spreading the impulse rapidly from cell to cell to trigger the contraction of the entire heart.<ref name="CNX2014"/>

There are specific [[Bioinformatics#Gene and protein expression|proteins expressed]] in cardiac muscle cells.<ref>{{Cite web|url=https://www.proteinatlas.org/humanproteome/heart|title=The human proteome in heart |series=The Human Protein Atlas|website=www.proteinatlas.org|access-date=2017-09-29|archive-date=9 November 2018|archive-url=https://web.archive.org/web/20181109191813/http://www.proteinatlas.org/humanproteome/heart|url-status=live}}</ref><ref>{{Cite journal|last1=Uhlén|first1=Mathias|last2=Fagerberg|first2=Linn|last3=Hallström|first3=Björn M.|last4=Lindskog|first4=Cecilia|last5=Oksvold|first5=Per|last6=Mardinoglu|first6=Adil|last7=Sivertsson|first7=Åsa|last8=Kampf|first8=Caroline|last9=Sjöstedt|first9=Evelina|s2cid=802377|date=2015-01-23|title=Tissue-based map of the human proteome|journal=Science|language=en|volume=347|issue=6220|article-number=1260419|doi=10.1126/science.1260419|issn=0036-8075|pmid=25613900}}</ref> These are mostly associated with muscle contraction, and bind with [[actin]], [[myosin]], [[tropomyosin]], and [[troponin]]. They include [[MYH6]], [[ACTC1]], [[TNNI3]], [[CDH2]] and [[Plakophilin-2|PKP2]]. Other proteins expressed are [[MYH7]] and [[LDB3]] that are also expressed in skeletal muscle.<ref>{{Cite journal|last1=Lindskog|first1=Cecilia|last2=Linné|first2=Jerker|last3=Fagerberg|first3=Linn|last4=Hallström|first4=Björn M.|last5=Sundberg|first5=Carl Johan|last6=Lindholm|first6=Malene|last7=Huss|first7=Mikael|last8=Kampf|first8=Caroline|last9=Choi|first9=Howard|date=2015-06-25|title=The human cardiac and skeletal muscle proteomes defined by transcriptomics and antibody-based profiling|journal=BMC Genomics|volume=16|issue=1 |page=475|doi=10.1186/s12864-015-1686-y|pmid=26109061|pmc=4479346|issn=1471-2164 |doi-access=free }}</ref>

=== Pericardium ===
{{Main|Pericardium}}
The pericardium is the sac that surrounds the heart. The tough outer surface of the pericardium is called the fibrous membrane. This is lined by a double inner membrane called the serous membrane that produces [[pericardial fluid]] to lubricate the surface of the heart.{{sfn|Gray's Anatomy|2008|p=959}} The part of the serous membrane attached to the fibrous membrane is called the parietal pericardium, while the part of the serous membrane attached to the heart is known as the visceral pericardium. The pericardium is present in order to lubricate its movement against other structures within the chest, to keep the heart's position stabilised within the chest, and to protect the heart from infection.<ref>{{Cite book|title=Principles of human anatomy|last=J.|first=Tortora, Gerard|date=2009|publisher=J. Wiley|others=Nielsen, Mark T. (Mark Thomas)|isbn=978-0-471-78931-4|edition=11th|location=Hoboken, NJ|oclc=213300667}}</ref>

===Coronary circulation===
[[File:Coronary arteries.svg|thumb|Arterial supply to the heart (red), with other areas labelled (blue).]]
{{main|Coronary circulation}}
Heart tissue, like all cells in the body, needs to be supplied with [[oxygen]], [[nutrient]]s and a way of removing [[metabolic waste]]s. This is achieved by the coronary circulation, which includes [[artery|arteries]], [[vein]]s, and [[lymph vessel|lymphatic vessels]]. Blood flow through the coronary vessels occurs in peaks and troughs relating to the heart muscle's relaxation or contraction.<ref name="CNX2014"/>

Heart tissue receives blood from two arteries which arise just above the aortic valve. These are the [[left main coronary artery]] and the [[right coronary artery]]. The left main coronary artery splits shortly after leaving the aorta into two vessels, the [[left anterior descending]] and the [[left circumflex artery]]. The left anterior descending artery supplies heart tissue and the front, outer side, and septum of the left ventricle. It does this by branching into smaller arteries—diagonal and septal branches. The left circumflex supplies the back and underneath of the left ventricle. The right coronary artery supplies the right atrium, right ventricle, and lower posterior sections of the left ventricle. The right coronary artery also supplies blood to the atrioventricular node (in about 90% of people) and the sinoatrial node (in about 60% of people). The right coronary artery runs in a groove at the back of the heart and the left anterior descending artery runs in a groove at the front. There is significant variation between people in the anatomy of the arteries that supply the heart.{{sfn|Davidson's|2010|p=525}} The arteries divide at their furthest reaches into smaller branches that join at the edges of each arterial distribution.<ref name="CNX2014"/>

The [[coronary sinus]] is a large vein that drains into the right atrium, and receives most of the venous drainage of the heart. It receives blood from the [[great cardiac vein]] (receiving the left atrium and both ventricles), the [[posterior cardiac vein]] (draining the back of the left ventricle), the [[middle cardiac vein]] (draining the bottom of the left and right ventricles), and [[small cardiac vein]]s.{{sfn|Gray's Anatomy|2008|p=981}} The [[anterior cardiac veins]] drain the front of the right ventricle and drain directly into the right atrium.<ref name="CNX2014"/>

Small lymphatic networks called [[plexus]]es exist beneath each of the three layers of the heart. These networks collect into a main left and a main right trunk, which travel up the groove between the ventricles that exists on the heart's surface, receiving smaller vessels as they travel up. These vessels then travel into the atrioventricular groove, and receive a third vessel which drains the section of the left ventricle sitting on the diaphragm. The left vessel joins with this third vessel, and travels along the pulmonary artery and left atrium, ending in the [[inferior tracheobronchial node]]. The right vessel travels along the right atrium and the part of the right ventricle sitting on the diaphragm. It usually then travels in front of the ascending aorta and then ends in a brachiocephalic node.{{sfn|Gray's Anatomy|2008|p=982}}

===Nerve supply===
[[File:2032 Automatic Innervation.jpg|thumb|Autonomic innervation of the heart]]
The heart receives nerve signals from the [[vagus nerve]] and from nerves arising from the [[sympathetic trunk]]. These nerves act to influence, but not control, the heart rate. [[Sympathetic nervous system|Sympathetic nerves]] also influence the force of heart contraction.{{sfn|Davidson's|2010|p=526}} Signals that travel along these nerves arise from two paired [[cardiovascular centre]]s in the [[medulla oblongata]]. The vagus nerve of the [[parasympathetic nervous system]] acts to decrease the heart rate, and nerves from the [[sympathetic trunk]] act to increase the heart rate.<ref name="CNX2014"/> These nerves form a network of nerves that lies over the heart called the [[cardiac plexus]].<ref name="CNX2014"/>{{sfn|Gray's Anatomy|2008|p=982}}

The vagus nerve is a long, wandering nerve that emerges from the [[brainstem]] and provides parasympathetic stimulation to a large number of organs in the thorax and abdomen, including the heart.{{sfn|Gray's Anatomy|2008|p=945}} The nerves from the sympathetic trunk emerge through the T1–T4 [[thoracic ganglia]] and travel to both the sinoatrial and atrioventricular nodes, as well as to the atria and ventricles. The ventricles are more richly innervated by sympathetic fibers than parasympathetic fibers. Sympathetic stimulation causes the release of the neurotransmitter [[norepinephrine]] (also known as [[noradrenaline]]) at the [[neuromuscular junction]] of the cardiac nerves{{Citation needed|date=October 2024}}. This shortens the repolarisation period, thus speeding the rate of depolarisation and contraction, which results in an increased heart rate. It opens chemical or ligand-gated sodium and calcium ion channels, allowing an influx of [[cation|positively charged ions]].<ref name="CNX2014"/> Norepinephrine binds to the [[beta-1 adrenergic receptor|beta–1 receptor]].<ref name="CNX2014"/>

==Development==
{{anchor|Early development|Heart development|Development|Embryology}}
{{main|Heart development|Human embryogenesis}}
[[File:2037 Embryonic Development of Heart.jpg|thumb|right|450px|Development of the human heart during the first eight weeks (top) and the formation of the heart chambers (bottom). In this figure, the blue and red colors represent blood inflow and outflow (not venous and arterial blood). Initially, all venous blood flows from the tail/atria to the ventricles/head, a very different pattern from that of an adult.<ref name="CNX2014"/>]]

The heart is the first functional organ to develop and starts to beat and pump blood at about three weeks into [[human embryogenesis|embryogenesis]]. This early start is crucial for subsequent embryonic and [[prenatal development]].

The heart derives from [[splanchnopleuric mesenchyme]] in the neural plate which forms the [[cardiogenic region]]. Two [[endocardial tubes]] form here that fuse to form a primitive heart tube known as the [[tubular heart]].<ref>{{cite web |url=http://www.meddean.luc.edu/lumen/MedEd/GrossAnatomy/thorax0/heartdev/main_fra.html |title=Main Frame Heart Development |publisher=Meddean.luc.edu |access-date=2010-10-17 |url-status=live |archive-url=http://webarchive.loc.gov/all/20011116192836/http://www.meddean.luc.edu/lumen/meded/grossanatomy/thorax0/heartdev/main_fra.html |archive-date=16 November 2001}}</ref> Between the third and fourth week, the heart tube lengthens, and begins to fold to form an S-shape within the pericardium. This places the chambers and major vessels into the correct alignment for the developed heart. Further development will include the formation of the septa and the valves and the remodeling of the heart chambers. By the end of the fifth week, the septa are complete, and by the ninth week, the heart valves are complete.<ref name="CNX2014"/>

Before the fifth week, there is an opening in the fetal heart known as the [[Foramen ovale (heart)|foramen ovale]]. The foramen ovale allowed blood in the fetal heart to pass directly from the right atrium to the left atrium, allowing some blood to bypass the lungs. Within seconds after birth, a flap of tissue known as the [[septum primum]] that previously acted as a valve closes the foramen ovale and establishes the typical cardiac circulation pattern. A depression in the surface of the right atrium remains where the foramen ovale was, called the fossa ovalis.<ref name="CNX2014"/>

The [[embryo]]nic heart begins beating at around 22 days after conception (5 weeks after the last normal menstrual period, LMP). It starts to beat at a rate near to the mother's which is about 75–80 [[beats per minute]] (bpm). The embryonic heart rate then accelerates and reaches a peak rate of 165–185 bpm early in the early 7th week (early 9th week after the LMP).<ref>{{cite journal |last1=DuBose |first1=T.J. |last2=Cunyus |first2=J.A. |last3=Johnson |first3=L. |s2cid=72955922 |title= Embryonic Heart Rate and Age|journal= J Diagn Med Sonography|year=1990|volume= 6|doi=10.1177/875647939000600306 |pages=151–157|issue=3|citeseerx=10.1.1.860.9613 }}</ref><ref name="Fetal Sonography">DuBose, T.J. (1996) ''Fetal Sonography'', pp. 263–274; Philadelphia: WB Saunders {{ISBN|0-7216-5432-0}}</ref> After 9 weeks (start of the [[fetal]] stage) it starts to decelerate, slowing to around 145 (±25) bpm at birth. There is no difference in female and male heart rates before birth.<ref>DuBose, Terry J. (26 July 2011) [http://www.obgyn.net/articles/sex-heart-rate-and-age Sex, Heart Rate and Age] {{webarchive|url=https://web.archive.org/web/20140502000841/http://www.obgyn.net/articles/sex-heart-rate-and-age |date=2 May 2014 }}. obgyn.net</ref>{{Clear}}

==Physiology==
{{anchor|Function}}{{main|Cardiac physiology}}

===Blood flow===
[[File:Latidos.gif|thumb|left|Blood flow through the valves]]
[[File:Flow through the Heart.webm|thumb|Blood flow through the heart]]
[[File:Schematic 3D illustration of blood flow through the heart.ogg|thumb|Video explanation of blood flow through the heart]]
The heart functions as a pump in the [[circulatory system]] to provide a continuous [[blood flow|flow of blood]] throughout the body. This circulation consists of the [[systemic circulation]] to and from the body and the [[pulmonary circulation]] to and from the lungs. Blood in the pulmonary circulation exchanges [[carbon dioxide]] for oxygen in the lungs through the process of [[breathing|respiration]]. The systemic circulation then transports oxygen to the body and returns carbon dioxide and relatively deoxygenated blood to the heart for transfer to the lungs.<ref name="CNX2014"/>

The [[#Right heart|right heart]] collects deoxygenated blood from two large veins, the [[superior vena cava|superior]] and [[inferior vena cava|inferior]] [[venae cavae]]. Blood collects in the right and left atrium continuously.<ref name="CNX2014"/> The superior vena cava drains blood from above the [[thoracic diaphragm|diaphragm]] and empties into the upper back part of the right atrium. The inferior vena cava drains the blood from below the diaphragm and empties into the back part of the atrium below the opening for the superior vena cava. Immediately above and to the middle of the opening of the inferior vena cava is the opening of the thin-walled coronary sinus.<ref name="CNX2014"/> Additionally, the [[coronary sinus]] returns deoxygenated blood from the myocardium to the right atrium. The blood collects in the right atrium. When the right atrium contracts, the blood is pumped through the [[tricuspid valve]] into the right ventricle. As the right ventricle contracts, the tricuspid valve closes and the blood is pumped into the pulmonary trunk through the pulmonary valve. The pulmonary trunk divides into pulmonary arteries and progressively smaller arteries throughout the lungs, until it reaches [[capillaries]]. As these pass by [[Pulmonary alveolus|alveoli]] carbon dioxide is [[gas exchange|exchanged]] for oxygen. This happens through the passive process of [[diffusion]].

In the [[#Left heart|left heart]], oxygenated blood is returned to the left atrium via the pulmonary veins. It is then pumped into the left ventricle through the [[mitral valve]] and into the aorta through the aortic valve for systemic circulation. The aorta is a large artery that branches into many smaller arteries, [[arteriole]]s, and ultimately capillaries. In the capillaries, oxygen and nutrients from blood are supplied to body cells for metabolism, and exchanged for carbon dioxide and waste products.<ref name="CNX2014"/> Capillary blood, now deoxygenated, travels into [[venule]]s and veins that ultimately collect in the superior and inferior vena cavae, and into the right heart.

====Cardiac cycle====
{{main|Cardiac cycle|Systole|Diastole}}
[[File:2027 Phases of the Cardiac Cycle.jpg|thumb|The cardiac cycle as correlated to the ECG]]

The cardiac cycle is the sequence of events in which the heart contracts and relaxes with every heartbeat.{{sfn|Guyton & Hall|2011|pp=105–107}} The period of time during which the ventricles contract, forcing blood out into the aorta and main pulmonary artery, is known as [[systole]], while the period during which the ventricles relax and refill with blood is known as [[diastole]]. The atria and ventricles work in concert, so in systole when the ventricles are contracting, the atria are relaxed and collecting blood. When the ventricles are relaxed in diastole, the atria contract to pump blood to the ventricles. This coordination ensures blood is pumped efficiently to the body.<ref name="CNX2014"/>

At the beginning of the cardiac cycle, the ventricles are relaxing. As they do so, they are filled by blood passing through the open [[Mitral valve|mitral]] and [[Tricuspid valve|tricuspid]] valves. After the ventricles have completed most of their filling, the atria contract, forcing further blood into the ventricles and priming the pump. Next, the ventricles start to contract. As the pressure rises within the cavities of the ventricles, the mitral and tricuspid valves are forced shut. As the pressure within the ventricles rises further, exceeding the pressure with the aorta and pulmonary arteries, the aortic and pulmonary valves open. Blood is ejected from the heart, causing the pressure within the ventricles to fall. Simultaneously, the atria refill as blood flows into the right atrium through the superior and [[inferior vena cava]]e, and into the left atrium through the pulmonary veins. Finally, when the pressure within the ventricles falls below the pressure within the aorta and pulmonary arteries, the aortic and pulmonary valves close. The ventricles start to relax, the mitral and tricuspid valves open, and the cycle begins again.{{sfn|Guyton & Hall|2011|pp=105–107}}

====Cardiac output====
{{main|Cardiac output}}
[[File:2029 Cardiac Cycle vs Heart Sounds.jpg|thumb|The x-axis reflects time with a recording of the heart sounds. The y-axis represents pressure.<ref name="CNX2014"/>]]
Cardiac output (CO) is a measurement of the amount of blood pumped by each ventricle (stroke volume) in one minute. This is calculated by multiplying the stroke volume (SV) by the beats per minute of the heart rate (HR). So that: CO = SV x HR.<ref name="CNX2014"/>
The cardiac output is normalized to body size through [[body surface area]] and is called the [[cardiac index]].

The average cardiac output, using an average stroke volume of about 70mL, is 5.25 L/min, with a normal range of 4.0–8.0 L/min.<ref name="CNX2014"/> The stroke volume is normally measured using an [[echocardiogram]] and can be influenced by the size of the heart, physical and mental condition of the individual, [[sex]], [[Myocardial contractility|contractility]], duration of contraction, [[preload (cardiology)|preload]] and [[afterload]].<ref name="CNX2014"/>

[[Preload (cardiology)|Preload]] refers to the filling pressure of the atria at the end of diastole, when the ventricles are at their fullest. A main factor is how long it takes the ventricles to fill: if the ventricles contract more frequently, then there is less time to fill and the preload will be less.<ref name="CNX2014"/> Preload can also be affected by a person's blood volume. The force of each contraction of the heart muscle is proportional to the preload, described as the [[Frank-Starling mechanism]]. This states that the force of contraction is directly proportional to the initial length of muscle fiber, meaning a ventricle will contract more forcefully, the more it is stretched.<ref name="CNX2014" />{{sfn|Guyton & Hall|2011|pp=110–113}}

[[Afterload]], or how much pressure the heart must generate to eject blood at systole, is influenced by [[vascular resistance]]. It can be influenced by narrowing of the heart valves ([[stenosis]]) or contraction or relaxation of the peripheral blood vessels.<ref name="CNX2014"/>

The strength of heart muscle contractions controls the stroke volume. This can be influenced positively or negatively by agents termed [[inotropes]].<ref name="BERRY2010">{{cite journal|last1=Berry|first1=William|last2=McKenzie|first2=Catherine|title=Use of inotropes in critical care|journal=Clinical Pharmacist|date=1 January 2010|volume=2|page=395|url=http://www.pharmaceutical-journal.com/learning/learning-article/use-of-inotropes-in-critical-care/11049283.article|url-status=live|archive-url=https://web.archive.org/web/20161128052534/http://www.pharmaceutical-journal.com/learning/learning-article/use-of-inotropes-in-critical-care/11049283.article|archive-date=28 November 2016}}</ref> These agents can be a result of changes within the body, or be given as drugs as part of treatment for a medical disorder, or as a form of [[life support]], particularly in [[intensive care unit]]s. Inotropes that increase the force of contraction are "positive" inotropes, and include [[sympathetic nervous system|sympathetic]] agents such as [[adrenaline]], [[noradrenaline]] and [[dopamine]].<ref name=OH2010>{{cite book|author= Bersten, Andrew|title=Oh's Intensive Care Manual|date=2013|publisher=Elsevier Health Sciences|location=London|isbn=978-0-7020-4762-6|pages=912–922|edition=7th}}</ref> "Negative" inotropes decrease the force of contraction and include [[calcium channel blocker]]s.<ref name=BERRY2010 />

===Electrical conduction===
{{Main|Electrical conduction system of the heart}}
[[File:ECG principle slow.gif|275px|thumb|Transmission of a [[cardiac action potential]] through the heart's conduction system]]

The normal rhythmical heart beat, called [[sinus rhythm]], is established by the heart's own pacemaker, the [[sinoatrial node]] (also known as the sinus node or the SA node). Here an electrical signal is created that travels through the heart, causing the heart muscle to contract. The sinoatrial node is found in the upper part of the [[right atrium]] near to the junction with the superior vena cava.<ref>{{cite book|last1=Pocock|first1=Gillian|title=Human Physiology|date=2006|publisher=Oxford University Press|isbn=978-0-19-856878-0|page=266|edition=Third}}</ref> The electrical signal generated by the sinoatrial node travels through the right atrium in a radial way that is not completely understood. It travels to the left atrium via [[Bachmann's bundle]], such that the muscles of the left and right atria contract together.<ref>{{cite journal |last=Antz |first=Matthias |year=1998 |title=Electrical Conduction Between the Right Atrium and the Left Atrium via the Musculature of the Coronary Sinus |journal=Circulation |volume=98 |issue=17 |pages=1790–1795 |doi=10.1161/01.CIR.98.17.1790 |pmid=9788835 |display-authors=etal|doi-access=free }}</ref><ref>{{cite journal |last=De Ponti |first=Roberto |year=2002 |title=Electroanatomic Analysis of Sinus Impulse Propagation in Normal Human Atria |journal=Journal of Cardiovascular Electrophysiology |volume=13 |issue=1 |pages=1–10 |doi=10.1046/j.1540-8167.2002.00001.x |pmid=11843475 |s2cid=1705535 |display-authors=etal}}</ref><ref>{{cite web |url=http://www.medterms.com/script/main/art.asp?articlekey=5402 |title=Definition of SA node |publisher=MedicineNet.com |date=27 April 2011 |access-date=7 June 2012 |url-status=live |archive-url=https://web.archive.org/web/20120801181101/http://www.medterms.com/script/main/art.asp?articlekey=5402 |archive-date=1 August 2012}}</ref> The signal then travels to the [[atrioventricular node]]. This is found at the bottom of the right atrium in the [[atrioventricular septum]], the boundary between the right atrium and the left ventricle. The septum is part of the [[cardiac skeleton]], tissue within the heart that the electrical signal cannot pass through, which forces the signal to pass through the atrioventricular node only.<ref name="CNX2014" /> The signal then travels along the [[bundle of His]] to left and right [[bundle branches]] through to the ventricles of the heart. In the ventricles the signal is carried by specialized tissue called the [[Purkinje fibers]] which then transmit the electric charge to the heart muscle.<ref>{{cite web |url=http://biology.about.com/library/organs/heart/blpurkinje.htm |title=Purkinje Fibers |publisher=About.com |date=9 April 2012 |access-date=7 June 2012 |url-status=live |archive-url=https://web.archive.org/web/20120414214214/http://biology.about.com/library/organs/heart/blpurkinje.htm |archive-date=14 April 2012}}</ref>

[[image:ConductionsystemoftheheartwithouttheHeart-en.svg|right|thumb|275px|Conduction system of the heart]]

===Heart rate===
{{main|Heart rate}}{{listen|filename=Emily's racing heartbeat.wav|title=A racing heartbeat|description=Heart sounds of a 16 year old girl immediately after running, with a heart rate of 186 BPM.|format=[[wav]]}}[[File:2020 SA Node Tracing.jpg|thumb|The prepotential is due to a slow influx of sodium ions until the threshold is reached followed by a rapid depolarisation and repolarisation. The prepotential accounts for the membrane reaching threshold and initiates the spontaneous depolarisation and contraction of the cell; there is no resting potential.<ref name="CNX2014"/>]]

The normal [[resting heart rate]] is called the [[sinus rhythm]], created and sustained by the [[sinoatrial node]], a group of pacemaking cells found in the wall of the right atrium. Cells in the sinoatrial node do this by creating an [[action potential]]. The [[cardiac action potential]] is created by the movement of specific [[electrolyte]]s into and out of the pacemaker cells. The action potential then spreads to nearby cells.{{sfn|Guyton & Hall|2011|pp=115–120}}

When the sinoatrial cells are resting, they have a negative charge on their membranes. A rapid influx of [[sodium]] ions causes the membrane's charge to become positive; this is called [[depolarisation]] and occurs spontaneously.<ref name="CNX2014"/> Once the cell has a sufficiently high charge, the sodium channels close and [[calcium]] ions then begin to enter the cell, shortly after which [[potassium]] begins to leave it. All the ions travel through [[ion channels]] in the membrane of the sinoatrial cells. The potassium and calcium start to move out of and into the cell only once it has a sufficiently high charge, and so are called [[voltage-gated calcium channel|voltage-gated]]. Shortly after this, the calcium channels close and [[potassium channels]] open, allowing potassium to leave the cell. This causes the cell to have a negative resting charge and is called [[repolarization|repolarisation]]. When the membrane potential reaches approximately −60 mV, the potassium channels close and the process may begin again.<ref name="CNX2014"/>

The ions move from areas where they are concentrated to where they are not. For this reason sodium moves into the cell from outside, and potassium moves from within the cell to outside the cell. Calcium also plays a critical role. Their influx through slow channels means that the sinoatrial cells have a prolonged "plateau" phase when they have a positive charge. A part of this is called the [[absolute refractory period]]. Calcium ions also combine with the regulatory protein [[troponin C]] in the [[troponin complex]] to enable [[muscle contraction|contraction]] of the cardiac muscle, and separate from the protein to allow relaxation.<ref name="davis">{{cite journal| title=Ca<sup>2+</sup> exchange with troponin C and cardiac muscle dynamics |last1=Davis |first1=J.P. |last2=Tikunova |first2=S.B. | journal=Cardiovascular Research | year=2008 | volume=77 | issue=4 | pages=619–626 | doi=10.1093/cvr/cvm098 | pmid=18079104 | doi-access=free }}</ref>

The adult resting heart rate ranges from 60 to 100 bpm. The resting heart rate of a [[neonate|newborn]] can be 129 beats per minute (bpm) and this gradually decreases until maturity.<ref>{{cite journal|title=Resting pulse rate reference data for children, adolescents and adults, United States 1999–2008|journal=National Health Statistics Reports|issue=41|pages=1–16|url=https://www.cdc.gov/nchs/data/nhsr/nhsr041.pdf|pmid=21905522|year=2011|last1=Ostchega|first1=Y|last2=Porter|first2=K.S.|last3=Hughes|first3=J|last4=Dillon|first4=C.F.|last5=Nwankwo|first5=T|url-status=live|archive-url=https://web.archive.org/web/20170623030620/https://www.cdc.gov/nchs/data/nhsr/nhsr041.pdf|archive-date=23 June 2017}}</ref> An athlete's heart rate can be lower than 60 bpm. During exercise the rate can be 150 bpm with maximum rates reaching from 200 to 220 bpm.<ref name="CNX2014"/>

====Influences====
<!-- Nerves-->The normal [[sinus rhythm]] of the heart, giving the resting heart rate, is influenced by a number of factors. The [[cardiovascular centre]]s in the brainstem control the sympathetic and parasympathetic influences to the heart through the vagus nerve and sympathetic trunk.<ref name=GUYTONHALL2005>{{cite book|last2=Hall|first1=Arthur C. |last1=Guyton |first2=John E.|title=Textbook of medical physiology|date=2005|publisher=W.B. Saunders|location=Philadelphia|isbn=978-0-7216-0240-0|pages=116–122|edition=11th}}</ref> These cardiovascular centres receive input from a series of receptors including [[baroreceptor]]s, sensing the stretching of blood vessels and [[chemoreceptor]]s, sensing the amount of oxygen and carbon dioxide in the blood and its pH. Through a series of reflexes these help regulate and sustain blood flow.<ref name="CNX2014"/>

<!--Baroreceptors-->Baroreceptors are stretch receptors located in the [[aortic sinus]], [[carotid body|carotid bodies]], the venae cavae, and other locations, including pulmonary vessels and the right side of the heart itself. Baroreceptors fire at a rate determined by how much they are stretched,{{sfn|Guyton & Hall|2011|p=208}} which is influenced by blood pressure, level of physical activity, and the relative distribution of blood. With increased pressure and stretch, the rate of baroreceptor firing increases, and the cardiac centers decrease sympathetic stimulation and increase parasympathetic stimulation. As pressure and stretch decrease, the rate of baroreceptor firing decreases, and the cardiac centers increase sympathetic stimulation and decrease parasympathetic stimulation.<ref name="CNX2014"/> There is a similar reflex, called the atrial reflex or [[Bainbridge reflex]], associated with varying rates of blood flow to the atria. Increased venous return stretches the walls of the atria where specialized baroreceptors are located. However, as the atrial baroreceptors increase their rate of firing and as they stretch due to the increased blood pressure, the cardiac center responds by increasing sympathetic stimulation and inhibiting parasympathetic stimulation to increase heart rate. The opposite is also true.<ref name="CNX2014"/> Chemoreceptors present in the carotid body or adjacent to the aorta in an aortic body respond to the blood's oxygen, carbon dioxide levels. Low oxygen or high carbon dioxide will stimulate firing of the receptors.{{sfn|Guyton & Hall|2011|p=212}}

<!--Other-->Exercise and fitness levels, age, body temperature, [[basal metabolic rate]], and even a person's emotional state can all affect the heart rate. High levels of the hormones [[epinephrine]], norepinephrine, and [[thyroid hormone]]s can increase the heart rate. The levels of electrolytes including calcium, potassium, and sodium can also influence the speed and regularity of the heart rate; [[hypoxemia|low blood oxygen]], low [[blood pressure]] and [[dehydration]] may increase it.<ref name="CNX2014"/>

==Clinical significance==
===Diseases===
{{multiple image
| align = right
| direction = vertical
| image1 = Doctors stethoscope 1.jpg
| width1 = 230
| caption1 = The stethoscope is used for [[auscultation]] of the heart, and is one of the most iconic symbols for [[medicine]]. A number of diseases can be detected primarily by listening for [[heart murmur]]s.
| image2 = 2113ab Atherosclerosis.jpg
| width2 = 230
| caption2 = [[Atherosclerosis]] is a condition affecting the [[circulatory system]]. If the [[coronary arteries]] are affected, [[angina pectoris]] may result or at worse a [[heart attack]].
}}

[[Cardiovascular disease]]s, which include diseases of the heart, are the leading cause of death worldwide.<ref name="WHOfacts">{{Cite web|url=https://www.who.int/mediacentre/factsheets/fs317/en/|title=Cardiovascular diseases (CVDs)|website=World Health Organization|language=en-GB|access-date=2016-03-09|url-status=live|archive-url=https://web.archive.org/web/20160310222948/http://www.who.int/mediacentre/factsheets/fs317/en/|archive-date=10 March 2016}}</ref> The majority of cardiovascular disease is noncommunicable and related to lifestyle and other factors, becoming more prevalent with ageing.<ref name="WHOfacts" /> Heart disease is a major cause of death, accounting for an average of 30% of all deaths in 2008, globally.<ref name="WHO CVD 2013" /> This rate varies from a lower 28% to a high 40% in [[World Bank high-income economy|high-income countries]].<ref name="Harrisons" /> Doctors that specialise in the heart are called [[cardiologist]]s. Many other medical professionals are involved in treating diseases of the heart, including [[Physician|doctors]], [[cardiothoracic surgeon]]s, [[intensivist]]s, and [[allied health profession|allied health practitioners]] including [[physiotherapist]]s and [[dietician]]s.<ref>{{Cite web|url=http://www.heart.org/HEARTORG/Conditions/HeartFailure/LivingWithHeartFailureAndAdvancedHF/Your-Heart-Failure-Healthcare-Team_UCM_306361_Article.jsp|title=Your Heart Failure Healthcare Team|website=www.heart.org|access-date=2016-03-09|url-status=live|archive-url=https://web.archive.org/web/20160310073427/http://www.heart.org/HEARTORG/Conditions/HeartFailure/LivingWithHeartFailureAndAdvancedHF/Your-Heart-Failure-Healthcare-Team_UCM_306361_Article.jsp|archive-date=10 March 2016}}</ref>

==== Ischemic heart disease ====<!--Heart attack / AMI-->
{{main|Coronary artery disease}}

Coronary artery disease, also known as ischemic heart disease, is caused by [[atherosclerosis]]—a build-up of fatty material along the inner walls of the arteries. These fatty deposits known as atherosclerotic plaques [[stenosis|narrow]] the coronary arteries, and if severe may reduce blood flow to the heart.<ref name="WHFdiseases">{{Cite web|url=http://www.world-heart-federation.org/cardiovascular-health/heart-disease/different-heart-diseases/|title=Different heart diseases|website=World Heart Federation|access-date=2016-03-09|url-status=live|archive-url=https://web.archive.org/web/20160312102709/http://www.world-heart-federation.org/cardiovascular-health/heart-disease/different-heart-diseases/|archive-date=12 March 2016}}</ref> If a narrowing (or stenosis) is relatively minor then the patient may not experience any symptoms. Severe narrowings may cause chest pain ([[angina]]) or breathlessness during exercise or even at rest. The thin covering of an atherosclerotic plaque can rupture, exposing the fatty centre to the circulating blood. In this case a clot or thrombus can form, blocking the artery, and restricting blood flow to an area of heart muscle causing a myocardial infarction (a heart attack) or [[unstable angina]].{{sfn|Harrison's|2011|p=1501}} In the worst case this may cause [[cardiac arrest]], a sudden and utter loss of output from the heart.{{sfn|Davidson's|2010|p=554}} [[Obesity]], [[high blood pressure]], uncontrolled [[diabetes]], smoking and high [[cholesterol]] can all increase the risk of developing atherosclerosis and coronary artery disease.<ref name="WHOfacts" /><ref name="WHFdiseases" />

==== Heart failure ====<!--Heart failure-->
{{main|Heart failure}}
Heart failure is defined as a condition in which the heart is unable to pump enough blood to meet the demands of the body.<ref name=":2" /> Patients with [[heart failure]] may experience breathlessness especially when lying flat, as well as ankle swelling, known as [[Peripheral edema|peripheral oedema]]. Heart failure is the result of many diseases affecting the heart, but is most commonly associated with [[Coronary artery disease|ischemic heart disease]], [[valvular heart disease]], or high blood pressure. Less common causes include various [[Cardiomyopathy|cardiomyopathies]]. Heart failure is frequently associated with weakness of the heart muscle in the ventricles (systolic heart failure), but can also be seen in patients with heart muscle that is strong but stiff (diastolic heart failure). The condition may affect the left ventricle (causing predominantly breathlessness), the right ventricle (causing predominantly swelling of the legs and an elevated [[jugular venous pressure]]), or both ventricles. Patients with heart failure are at higher risk of developing dangerous heart rhythm disturbances or [[Heart arrhythmia|arrhythmias]].<ref name=":2" />

==== Cardiomyopathies ====<!-- Cardiomyopathy -->
{{main|Cardiomyopathy}}Cardiomyopathies are diseases affecting the muscle of the heart. Some cause abnormal thickening of the heart muscle ([[hypertrophic cardiomyopathy]]), some cause the heart to abnormally expand and weaken ([[dilated cardiomyopathy]]), some cause the heart muscle to become stiff and unable to fully relax between contractions ([[restrictive cardiomyopathy]]) and some make the heart prone to abnormal heart rhythms ([[arrhythmogenic cardiomyopathy]]). These conditions are often genetic and can be [[Inherited disease|inherited]], but some such as dilated cardiomyopathy may be caused by damage from toxins such as alcohol. Some cardiomyopathies such as hypertrophic cardiomopathy are linked to a higher risk of sudden cardiac death, particularly in athletes.<ref name="CNX2014" /> Many cardiomyopathies can lead to heart failure in the later stages of the disease.<ref name=":2" />

==== Valvular heart disease ====<!-- Murmurs-->
{{main|Valvular heart disease}}{{listen|filename=Mitral Valve Prolapse.wav|title=Mitral Valve Prolapse murmur|description=Heart sounds of a 16 year old girl diagnosed with mitral valve prolapse and mitral regurgitation. Auscultating her heart, a systolic murmur and click is heard. Recorded with the stethoscope over the mitral valve.|format=[[wav]]}}Healthy heart valves allow blood to flow easily in one direction, and prevent it from flowing in the other direction. A diseased heart valve may have a narrow opening ([[stenosis]]), that restricts the flow of blood in the forward direction. A valve may otherwise be leaky, allowing blood to leak in the reverse direction ([[Regurgitation (circulation)|regurgitation]]). Valvular heart disease may cause breathlessness, blackouts, or chest pain, but may be asymptomatic and only detected on a routine examination by hearing abnormal heart sounds or a [[heart murmur]]. In the developed world, valvular heart disease is most commonly caused by degeneration secondary to old age, but may also be caused by infection of the heart valves ([[endocarditis]]). In some parts of the world [[Rheumatic Heart Disease|rheumatic heart disease]] is a major cause of valvular heart disease, typically leading to mitral or aortic stenosis and caused by the body's immune system reacting to a [[Group A streptococcal infection|streptococcal]] throat infection.<ref name=":4" />{{sfn|Davidson's|2010|pp=612–613}}

==== Cardiac arrhythmias ====<!-- Abnormalities of rhythm-->
{{main|Arrhythmia}}
{{Listen|filename=|title=An irregular heartbeat|description=Recording of heart sounds from a 16-year-old girl with a cardiac arrhythmia.|pos=[[wav]]}}
While in the healthy heart, waves of electrical impulses originate in the [[Sinoatrial node|sinus node]] before spreading to the rest of the atria, the [[atrioventricular node]], and finally the ventricles (referred to as a [[Sinus rhythm|normal sinus rhythm]]), this normal rhythm can be disrupted. Abnormal heart rhythms or arrhythmias may be asymptomatic or may cause palpitations, blackouts, or breathlessness. Some types of arrhythmia such as [[atrial fibrillation]] increase the long term risk of [[stroke]].<ref name=":3" />

Some arrhythmias cause the heart to beat abnormally slowly, referred to as a [[bradycardia]] or bradyarrhythmia. This may be caused by an [[Sick sinus syndrome|abnormally slow sinus node]] or damage within the cardiac conduction system ([[heart block]]).<ref name=":1" /> In other arrhythmias the heart may beat abnormally rapidly, referred to as a [[tachycardia]] or tachyarrhythmia. These arrhythmias can take many forms and can originate from different structures within the heart—some arise from the atria (e.g. [[atrial flutter]]), some from the atrioventricular node (e.g. [[AV nodal reentrant tachycardia|AV nodal re-entrant tachycardia]]) whilst others arise from the ventricles (e.g. [[ventricular tachycardia]]). Some tachyarrhythmias are caused by scarring within the heart (e.g. some forms of [[ventricular tachycardia]]), others by an irritable focus (e.g. focal [[atrial tachycardia]]), while others are caused by additional abnormal conduction tissue that has been present since birth (e.g. [[Wolff–Parkinson–White syndrome|Wolff-Parkinson-White syndrome]]). The most dangerous form of heart racing is [[ventricular fibrillation]], in which the ventricles quiver rather than contract, and which if untreated is rapidly fatal.<ref>{{Cite journal|last1=Blomström-Lundqvist|first1=Carina|last2=Scheinman|first2=Melvin M.|last3=Aliot|first3=Etienne M.|last4=Alpert|first4=Joseph S.|last5=Calkins|first5=Hugh|last6=Camm|first6=A. John|last7=Campbell|first7=W. Barton|last8=Haines|first8=David E.|last9=Kuck|first9=Karl H.|date=2003-10-14|title=ACC/AHA/ESC guidelines for the management of patients with supraventricular arrhythmias – executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the European Society of Cardiology Committee for Practice Guidelines (Writing Committee to Develop Guidelines for the Management of Patients With Supraventricular Arrhythmias)|journal=Circulation|volume=108|issue=15|pages=1871–1909|doi=10.1161/01.CIR.0000091380.04100.84|issn=1524-4539|pmid=14557344|doi-access=free}}</ref>

==== Pericardial disease ====<!-- Pericardium-->
The sac which surrounds the heart, called the pericardium, can become inflamed in a condition known as [[pericarditis]]. This condition typically causes chest pain that may spread to the back, and is often caused by a viral infection ([[Infectious mononucleosis|glandular fever]], [[cytomegalovirus]], or [[coxsackievirus]]). Fluid can build up within the pericardial sac, referred to as a [[pericardial effusion]]. Pericardial effusions often occur secondary to pericarditis, kidney failure, or tumours, and frequently do not cause any symptoms. However, large effusions or effusions which accumulate rapidly can compress the heart in a condition known as [[cardiac tamponade]], causing breathlessness and potentially fatal low blood pressure. Fluid can be removed from the pericardial space for diagnosis or to relieve tamponade using a syringe in a procedure called [[pericardiocentesis]].{{sfn|Davidson's|2010|pp=638–639}}

==== Congenital heart disease ====<!--Congenital disease-->
{{main|Congenital heart defect}}
Some people are born with hearts that are abnormal and these abnormalities are known as congenital heart defects. They may range from the relatively minor (e.g. [[patent foramen ovale]], arguably a variant of normal) to serious life-threatening abnormalities (e.g. [[hypoplastic left heart syndrome]]). Common abnormalities include those that affect the heart muscle that separates the two side of the heart (a "hole in the heart", e.g. [[ventricular septal defect]]). Other defects include those affecting the heart valves (e.g. [[Aortic stenosis|congenital aortic stenosis]]), or the main blood vessels that lead from the heart (e.g. [[coarctation of the aorta]]). More complex syndromes are seen that affect more than one part of the heart (e.g. [[Tetralogy of Fallot]]).

Some congenital heart defects allow blood that is low in oxygen that would normally be returned to the lungs to instead be pumped back to the rest of the body. These are known as [[Cyanotic heart defect|cyanotic congenital heart defects]] and are often more serious. Major congenital heart defects are often picked up in childhood, shortly after birth, or even before a child is born (e.g. [[Transposition of the great vessels|transposition of the great arteries]]), causing breathlessness and a lower rate of growth. More minor forms of congenital heart disease may remain undetected for many years and only reveal themselves in adult life (e.g., [[atrial septal defect]]).<ref>{{Cite journal|last1=Baumgartner|first1=Helmut|last2=Bonhoeffer|first2=Philipp|last3=De Groot|first3=Natasja M.S.|last4=de Haan|first4=Fokko|last5=Deanfield|first5=John Erik|last6=Galie|first6=Nazzareno|last7=Gatzoulis|first7=Michael A.|last8=Gohlke-Baerwolf|first8=Christa|last9=Kaemmerer|first9=Harald|date=December 2010|title=ESC Guidelines for the management of grown-up congenital heart disease (new version 2010)|journal=European Heart Journal|volume=31|issue=23|pages=2915–2957|doi=10.1093/eurheartj/ehq249|issn=1522-9645|pmid=20801927|doi-access=free}}</ref>{{sfn|Harrison's|2011|p=1458–65}}

==== Channelopathies ====
{{main|Channelopathy}}
[[Channelopathies]] can be categorized based on the organ system they affect. In the cardiovascular system, the electrical impulse required for each heart beat is provided by the [[electrochemical gradient]] of each heart cell. Because the beating of the heart depends on the proper movement of ions across the surface membrane, cardiac ion channelopathies form a major group of heart diseases.<ref>{{Cite journal |last=Marbán |first=Eduardo |date=2002-01-10 |title=Cardiac channelopathies |journal=Nature |volume=415 |issue=6868 |pages=213–218 |doi=10.1038/415213a |issn=0028-0836 |pmid=11805845|bibcode=2002Natur.415..213M |s2cid=4419017 }}</ref><ref>{{Cite journal |last=Marban |first=Eduardo |date=2003-07-01 |title=Cardiac Channelopathies |url=https://www.heartviews.org/article.asp?issn=1995-705X;year=2003;volume=4;issue=3;spage=4;epage=4;aulast=Marban;type=0 |journal=Heart Views |language=en |volume=4 |issue=3 |page=4 |issn=1995-705X}}</ref> Cardiac ion channelopathies may explain some of the cases of [[sudden death syndrome]] and [[sudden arrhythmic death syndrome]].<ref name="Skinner">{{cite journal |vauthors=Skinner JR, Winbo A, Abrams D, Vohra J, Wilde AA |title=Channelopathies That Lead to Sudden Cardiac Death: Clinical and Genetic Aspects |journal=Heart Lung Circ |volume=28 |issue=1 |pages=22–30 |date=January 2019 |pmid=30389366 |doi=10.1016/j.hlc.2018.09.007 |s2cid=53270374 |url=}}</ref> Long QT syndrome is the most common form of cardiac channelopathy.

* [[Long QT syndrome]] (LQTS) – Mostly hereditary. On EKG can be observed as longer corrected QT interval (QTc). Characterized by fainting, sudden, life-threatening heart rhythm disturbances – [[Torsades de pointes]] type ventricular tachycardia, ventricular fibrillation and risk of sudden cardiac death.<ref>{{Cite web |title=Long QT Syndrome |url=https://rarediseases.org/rare-diseases/romano-ward-syndrome/ |access-date=2022-11-19 |website=NORD (National Organization for Rare Disorders) |language=en-US}}</ref>
* [[Short QT syndrome]].
* [[Catecholaminergic polymorphic ventricular tachycardia]] (CPVT).<ref>{{Cite web |title=Catecholaminergic polymorphic ventricular tachycardia: MedlinePlus Genetics |url=https://medlineplus.gov/genetics/condition/catecholaminergic-polymorphic-ventricular-tachycardia/ |access-date=2022-11-19 |website=medlineplus.gov |language=en}}</ref>
* [[Progressive cardiac conduction defect]] (PCCD).<ref>{{Cite web |title=Progressive familial heart block: MedlinePlus Genetics |url=https://medlineplus.gov/genetics/condition/progressive-familial-heart-block/ |access-date=2022-11-19 |website=medlineplus.gov |language=en}}</ref>
* [[Benign early repolarization|Early repolarisation syndrome]] (BER) – common in younger and active people, especially men, because it is affected by higher [[testosterone]] levels, which cause increased potassium currents, which further causes an elevation of the [[J-point]] on the EKG. In very rare cases, it can lead to ventricular fibrillation and death.<ref>{{Cite journal |last1=Bourier |first1=Felix |last2=Denis |first2=Arnaud |last3=Cheniti |first3=Ghassen |last4=Lam |first4=Anna |last5=Vlachos |first5=Konstantinos |last6=Takigawa |first6=Masateru |last7=Kitamura |first7=Takeshi |last8=Frontera |first8=Antonio |last9=Duchateau |first9=Josselin |last10=Pambrun |first10=Thomas |last11=Klotz |first11=Nicolas |last12=Derval |first12=Nicolas |last13=Sacher |first13=Frédéric |last14=Jais |first14=Pierre |last15=Haissaguerre |first15=Michel |date=2018-11-27 |title=Early Repolarization Syndrome: Diagnostic and Therapeutic Approach |journal=Frontiers in Cardiovascular Medicine |volume=5 |page=169 |doi=10.3389/fcvm.2018.00169 |issn=2297-055X |pmc=6278243 |pmid=30542653|doi-access=free }}</ref>
* [[Brugada syndrome]] – a genetic disorder characterized by an abnormal EKG and is one of the most common causes of sudden cardiac death in young men.<ref>{{Cite web |title=Brugada syndrome: MedlinePlus Genetics |url=https://medlineplus.gov/genetics/condition/brugada-syndrome/ |access-date=2022-11-19 |website=medlineplus.gov |language=en}}</ref>

===Diagnosis===
Heart disease is diagnosed by the taking of a [[medical history]], a [[cardiac examination]], and further investigations, including [[blood test]]s, [[echocardiogram]]s, [[electrocardiograms]], and [[cardiac imaging|imaging]]. Other invasive procedures such as [[cardiac catheterisation]] can also play a role.{{sfn|Davidson's|2010|pp=527–534}}

====Examination====
{{Main|Cardiac examination|Heart sounds}}

The cardiac examination includes inspection, feeling the chest with the hands ([[palpation]]) and listening with a stethoscope ([[auscultation]]).<ref name="Davidsons2010_1">{{cite book|last1=Davidson|first1=Sir Stanley|last2=Colledge|first2=Nicki R.|last3=Walker|first3=Brian R.|last4=Ralston|first4=Stuart|title=Davidson's Principles and Practice of Medicine|date=2010|publisher=Churchill Livingstone/Elsevier|location=Edinburgh|isbn=978-0-7020-3084-0|pages=522–536|edition=21st}}</ref>{{sfn|Davidson's|2010|pp=522–536}} It involves assessment of [[medical sign|signs]] that may be visible on a person's hands (such as [[splinter haemorrhage]]s), joints and other areas. A person's pulse is taken, usually at the [[radial artery]] near the wrist, in order to assess for the rhythm and strength of the pulse. The [[blood pressure]] is taken, using either a manual or automatic [[sphygmomanometer]] or using [[Blood pressure#Invasive|a more invasive measurement]] from within the artery. Any elevation of the [[jugular vein|jugular venous pulse]] is noted. A person's [[chest]] is felt for any transmitted vibrations from the heart, and then listened to with a stethoscope.

====Heart sounds====
[[File:Apikal4D.gif|thumb|[[Echocardiography#Three-dimensional echocardiography|3D echocardiogram]] showing the mitral valve (right), tricuspid and mitral valves (top left) and aortic valve (top right).<br /> The closure of the heart valves causes the [[heart sounds]].]]
{{listen|filename=HROgg.ogg|title=Normal heart sounds|description=Normal heart sounds as heard with a [[stethoscope]]|format=[[Ogg]]}}
Typically, healthy hearts have only two audible [[heart sounds]], called S1 and S2. The [[first heart sound]] S1, is the sound created by the closing of the atrioventricular valves during ventricular contraction and is normally described as "lub". The [[second heart sound]], S2, is the sound of the semilunar valves closing during ventricular diastole and is described as "dub".<ref name="CNX2014"/> Each sound consists of two components, reflecting the slight difference in time as the two valves close.<ref name="TC2014">{{cite book|title=Clinical Examination|last1=Talley|first1=Nicholas J.|last2=O'Connor|first2=Simon|publisher=Churchill Livingstone|isbn=978-0-7295-4198-5|pages=76–82|year=2013}}</ref> S2 may [[split S2|split]] into two distinct sounds, either as a result of inspiration or different valvular or cardiac problems.<ref name=TC2014/> Additional heart sounds may also be present and these give rise to [[gallop rhythm]]s. A [[third heart sound]], S3 usually indicates an increase in ventricular blood volume. A [[fourth heart sound]] S4 is referred to as an atrial gallop and is produced by the sound of blood being forced into a stiff ventricle. The combined presence of S3 and S4 give a quadruple gallop.<ref name="CNX2014"/>
[[Heart murmur]]s are abnormal heart sounds which can be either related to disease or benign, and there are several kinds.{{sfn|Davidson's|2010|pp=556–559}} There are normally two heart sounds, and abnormal heart sounds can either be extra sounds, or "murmurs" related to the flow of blood between the sounds. Murmurs are graded by volume, from 1 (the quietest), to 6 (the loudest), and evaluated by their relationship to the heart sounds, position in the cardiac cycle, and additional features such as their radiation to other sites, changes with a person's position, the frequency of the sound as determined by the side of the [[stethoscope]] by which they are heard, and site at which they are heard loudest.{{sfn|Davidson's|2010|pp=556–559}} Murmurs may be caused by [[Valvular heart disease|damaged heart valves]] or congenital heart disease such as [[ventricular septal defect]]s, or may be heard in normal hearts. A different type of sound, a [[pericardial friction rub]] can be heard in cases of pericarditis where the inflamed membranes can rub together.

====Blood tests====
Blood tests play an important role in the diagnosis and treatment of many cardiovascular conditions.

<!--Specific tests-->[[Troponin]] is a sensitive [[biomarker]] for a heart with insufficient blood supply. It is released 4–6 hours after injury and usually peaks at about 12–24 hours.<ref name=OH2010 /> Two tests of troponin are often taken—one at the time of initial presentation and another within 3–6 hours,<ref>{{cite web|last1=Coven|first1=David|last2=Yang|first2=Eric|title=Acute Coronary Syndrome Workup|url=http://emedicine.medscape.com/article/1910735-workup|website=Medscape|access-date=14 August 2016|url-status=live|archive-url=https://web.archive.org/web/20160806121213/http://emedicine.medscape.com/article/1910735-workup|archive-date=6 August 2016}}</ref> with either a high level or a significant rise being diagnostic. A test for [[brain natriuretic peptide]] (BNP) can be used to evaluate for the presence of heart failure, and rises when there is increased demand on the left ventricle. These tests are considered [[biomarker]]s because they are highly specific for cardiac disease.{{sfn|Davidson's|2010|pp=531}} Testing for the [[CK-MB|MB form of creatine kinase]] provides information about the heart's blood supply, but is used less frequently because it is less specific and sensitive.{{sfn|Harrison's|2011|p=1534}}

<!--General tests-->Other blood tests are often taken to help understand a person's general health and risk factors that may contribute to heart disease. These often include a [[full blood count]] investigating for [[anaemia]], and [[basic metabolic panel]] that may reveal any disturbances in electrolytes. A [[coagulation screen]] is often required to ensure that the right level of anticoagulation is given. [[Lipid profile|Fasting lipids]] and [[fasting blood glucose]] (or an [[HbA1c]] level) are often ordered to evaluate a person's [[cholesterol]] and diabetes status, respectively.{{sfn|Davidson's|2010|pp=521–640}}

====Electrocardiogram====
{{main|Electrocardiography}}
[[File:2028 Cardiac Cycle vs Electrocardiogram.jpg|thumb|Cardiac cycle shown against ECG]]
Using surface electrodes on the body, it is possible to record the electrical activity of the heart. This tracing of the electrical signal is the electrocardiogram (ECG) or (EKG). An ECG is a [[bedside test]] and involves the placement of ten leads on the body. This produces a "12 lead" ECG (three extra leads are calculated mathematically, and one lead is [[Ground (electricity)|electrically ground]], or earthed).{{sfn|Davidson's|2010|pp=528–530}}

There are five prominent features on the ECG: the [[P wave (electrocardiography)|P wave]] (atrial depolarisation), the [[QRS complex]] (ventricular depolarisation){{efn|Depolarisation of the ventricles occurs concurrently, but is not significant enough to be detected on an ECG.{{sfn|Davidson's|2010|pp=528–530}}
}} and the [[T wave]] (ventricular repolarisation).<ref name="CNX2014"/> As the heart cells contract, they create a current that travels through the heart. A downward deflection on the ECG implies cells are becoming more positive in charge ("depolarising") in the direction of that lead, whereas an upward inflection implies cells are becoming more negative ("repolarising") in the direction of the lead. This depends on the position of the lead, so if a wave of depolarising moved from left to right, a lead on the left would show a negative deflection, and a lead on the right would show a positive deflection. The ECG is a useful tool in detecting [[arrythmia|rhythm disturbances]] and in detecting insufficient blood supply to the heart.{{sfn|Davidson's|2010|pp=528–530}} Sometimes abnormalities are suspected, but not immediately visible on the ECG. [[Cardiac stress test|Testing when exercising]] can be used to provoke an abnormality or an ECG can be worn for a longer period such as a 24-hour [[Holter monitor]] if a suspected rhythm abnormality is not present at the time of assessment.{{sfn|Davidson's|2010|pp=528–530}}

====Imaging====
{{Main|Cardiac imaging}}
Several [[medical imaging|imaging]] methods can be used to assess the anatomy and function of the heart, including [[ultrasound]] ([[echocardiography]]), [[angiography]], [[CT scan|CT]], [[MRI]], and [[Positron emission tomography|PET, scans]]. An echocardiogram is an ultrasound of the heart used to measure the heart's function, assess for valve disease, and look for any abnormalities. Echocardiography can be conducted by a probe on the chest ([[Transthoracic echocardiogram|transthoracic]]), or by a probe in the [[esophagus]] ([[Transesophageal echocardiogram|transesophageal]]). A typical echocardiography report will include information about the width of the valves noting any [[stenosis]], whether there is any backflow of blood ([[Regurgitation (circulation)|regurgitation]]) and information about the blood volumes at the end of systole and diastole, including an [[ejection fraction]], which describes how much blood is ejected from the left and right ventricles after systole. Ejection fraction can then be obtained by dividing the volume ejected by the heart (stroke volume) by the volume of the filled heart (end-diastolic volume).<ref>{{cite book|author1=Armstrong, William F.|author2=Ryan, Thomas|author3=Feigenbaum, Harvey|title=Feigenbaum's Echocardiography|url=https://books.google.com/books?id=LebU6zLrA8gC|year=2010|publisher=Lippincott Williams & Wilkins|isbn=978-0-7817-9557-9|url-status=live|archive-url=https://web.archive.org/web/20160423224258/https://books.google.com/books?id=LebU6zLrA8gC|archive-date=23 April 2016}}</ref> Echocardiograms can also be conducted under circumstances when the body is more stressed, in order to examine for signs of lack of blood supply. This [[cardiac stress test]] involves either direct exercise, or where this is not possible, injection of a drug such as [[dobutamine]].{{sfn|Davidson's|2010|pp=522–536}}

CT scans, [[chest X-rays]] and other forms of imaging can help evaluate the heart's size, evaluate for signs of [[pulmonary oedema]], and indicate whether there is [[pericardial effusion|fluid around the heart]]. They are also useful for evaluating the aorta, the major blood vessel which leaves the heart.{{sfn|Davidson's|2010|pp=522–536}}

===Treatment===
Diseases affecting the heart can be treated by a variety of methods including lifestyle modification, drug treatment, and surgery.

====Ischemic heart disease====
{{Main|Coronary artery disease|Coronary artery bypass surgery|Coronary stent}}Narrowings of the coronary arteries (ischemic heart disease) are treated to relieve symptoms of chest pain caused by a partially narrowed artery (angina pectoris), to minimise heart muscle damage when an artery is completely occluded ([[myocardial infarction]]), or to prevent a myocardial infarction from occurring. Medications to improve angina symptoms include [[Medical use of nitroglycerin|nitroglycerin]], [[beta blocker]]s, and calcium channel blockers, while preventative treatments include [[Antiplatelet drug|antiplatelets]] such as [[aspirin]] and [[statin]]s, lifestyle measures such as stopping smoking and weight loss, and treatment of risk factors such as high blood pressure and diabetes.<ref>{{Cite journal|last1=Authors/Task Force Members|last2=Piepoli|first2=Massimo F.|last3=Hoes|first3=Arno W.|last4=Agewall|first4=Stefan|last5=Albus|first5=Christian|last6=Brotons|first6=Carlos|last7=Catapano|first7=Alberico L.|last8=Cooney|first8=Marie-Therese|last9=Corrà|first9=Ugo|date=September 2016|title=2016 European Guidelines on cardiovascular disease prevention in clinical practice: The Sixth Joint Task Force of the European Society of Cardiology and Other Societies on Cardiovascular Disease Prevention in Clinical Practice (constituted by representatives of 10 societies and by invited experts) Developed with the special contribution of the European Association for Cardiovascular Prevention & Rehabilitation (EACPR)|journal=Atherosclerosis|volume=252|pages=207–274|doi=10.1016/j.atherosclerosis.2016.05.037|issn=1879-1484|pmid=27664503|url=http://orbi.ulg.ac.be/handle/2268/205776|doi-access=free|access-date=11 September 2018|archive-date=28 August 2021|archive-url=https://web.archive.org/web/20210828102950/https://orbi.uliege.be/handle/2268/205776|url-status=live}}</ref>

In addition to using medications, narrowed heart arteries can be treated by expanding the narrowings or redirecting the flow of blood to bypass an obstruction. This may be performed using a [[percutaneous coronary intervention]], during which narrowings can be expanded by passing small balloon-tipped wires into the coronary arteries, inflating the balloon to expand the narrowing, and sometimes leaving behind a metal scaffold known as a stent to keep the artery open.<ref name=":0">{{Cite journal|last1=Kolh|first1=Philippe|last2=Windecker|first2=Stephan|last3=Alfonso|first3=Fernando|last4=Collet|first4=Jean-Philippe|last5=Cremer|first5=Jochen|last6=Falk|first6=Volkmar|last7=Filippatos|first7=Gerasimos|last8=Hamm|first8=Christian|last9=Head|first9=Stuart J.|date=October 2014|title=2014 ESC/EACTS Guidelines on myocardial revascularization: the Task Force on Myocardial Revascularization of the European Society of Cardiology (ESC) and the European Association for Cardio-Thoracic Surgery (EACTS). Developed with the special contribution of the European Association of Percutaneous Cardiovascular Interventions (EAPCI)|journal=European Journal of Cardio-Thoracic Surgery|volume=46|issue=4|pages=517–592|doi=10.1093/ejcts/ezu366|issn=1873-734X|pmid=25173601|doi-access=free}}</ref>

If the narrowings in coronary arteries are unsuitable for treatment with a percutaneous coronary intervention, open surgery may be required. A [[Coronary artery bypass surgery|coronary artery bypass graft]] can be performed, whereby a blood vessel from another part of the body (the [[Great saphenous vein|saphenous vein]], [[radial artery]], or [[Internal thoracic artery|internal mammary artery]]) is used to redirect blood from a point before the narrowing (typically the [[aorta]]) to a point beyond the obstruction.<ref name=":0" />{{sfn|Davidson's|2010|pp=585–588, 614–623}}

==== Valvular heart disease ====
{{Main|Artificial heart valve}}Diseased heart valves that have become abnormally narrow or abnormally leaky may require surgery. This is traditionally performed as an open surgical procedure to replace the damaged heart valve with a tissue or metallic [[Artificial heart valve|prosthetic valve]]. In some circumstances, the [[Tricuspid valve|tricuspid]] or [[Mitral valve|mitral]] valves can be repaired [[Mitral valve repair|surgically]], avoiding the need for a valve replacement. Heart valves can also be treated percutaneously, using techniques that share many similarities with percutaneous coronary intervention. [[Transcatheter Aortic Valve Replacement|Transcatheter aortic valve replacement]] is increasingly used for patients consider very high risk for open valve replacement.<ref name=":4">{{Cite journal|last1=Vahanian|first1=Alec|last2=Alfieri|first2=Ottavio|last3=Andreotti|first3=Felicita|last4=Antunes|first4=Manuel J.|last5=Barón-Esquivias|first5=Gonzalo|last6=Baumgartner|first6=Helmut|last7=Borger|first7=Michael Andrew|last8=Carrel|first8=Thierry P.|last9=De Bonis|first9=Michele|date=October 2012|title=Guidelines on the management of valvular heart disease (version 2012): the Joint Task Force on the Management of Valvular Heart Disease of the European Society of Cardiology (ESC) and the European Association for Cardio-Thoracic Surgery (EACTS)|journal=European Journal of Cardio-Thoracic Surgery|volume=42|issue=4|pages=S1–44|doi=10.1093/ejcts/ezs455|issn=1873-734X|pmid=22922698|doi-access=free}}</ref>

==== Cardiac arrhythmias ====
{{Main|Heart arrhythmia|Radiofrequency ablation|Artificial cardiac pacemaker}}Abnormal heart rhythms ([[Heart arrhythmia|arrhythmias]]) can be treated using antiarrhythmic drugs. These may work by manipulating the flow of electrolytes across the cell membrane (such as [[calcium channel blocker]]s, [[sodium channel blocker]]s, [[amiodarone]], or [[digoxin]]), or modify the autonomic nervous system's effect on the heart ([[beta blocker]]s and [[atropine]]). In some arrhythmias such as atrial fibrillation which increase the risk of stroke, this risk can be reduced using anticoagulants such as [[warfarin]] or [[novel oral anticoagulants]].<ref name=":3">{{Cite journal|last1=Kirchhof|first1=Paulus|last2=Benussi|first2=Stefano|last3=Kotecha|first3=Dipak|last4=Ahlsson|first4=Anders|last5=Atar|first5=Dan|last6=Casadei|first6=Barbara|last7=Castella|first7=Manuel|last8=Diener|first8=Hans-Christoph|last9=Heidbuchel|first9=Hein|date=November 2016|title=2016 ESC Guidelines for the management of atrial fibrillation developed in collaboration with EACTS|journal=Europace|volume=18|issue=11|pages=1609–1678|doi=10.1093/europace/euw295|issn=1532-2092|pmid=27567465|doi-access=free}}</ref>

If medications fail to control an arrhythmia, another treatment option may be [[catheter ablation]]. In these procedures, wires are passed from a [[Femoral vein|vein]] or [[Femoral artery|artery]] in the leg to the heart to find the abnormal area of tissue that is causing the arrhythmia. The abnormal tissue can be intentionally damaged, or ablated, by [[Radiofrequency ablation|heating]] or [[Cryoablation|freezing]] to prevent further heart rhythm disturbances. Whilst the majority of arrhythmias can be treated using minimally invasive catheter techniques, some arrhythmias (particularly [[atrial fibrillation]]) can also be treated using open or [[Thoracoscopy|thoracoscopic]] surgery, either at the time of other cardiac surgery or as a standalone procedure. A [[cardioversion]], whereby an electric shock is used to stun the heart out of an abnormal rhythm, may also be used.

Cardiac devices in the form of [[Artificial cardiac pacemaker|pacemakers]] or [[Defibrillation|implantable defibrillators]] may also be required to treat arrhythmias. Pacemakers, comprising a small battery powered generator implanted under the skin and one or more leads that extend to the heart, are most commonly used to treat abnormally [[Bradycardia|slow heart rhythms]].<ref name=":1">{{Cite journal|last1=European Society of Cardiology (ESC)|last2=European Heart Rhythm Association (EHRA)|last3=Brignole|first3=Michele|last4=Auricchio|first4=Angelo|last5=Baron-Esquivias|first5=Gonzalo|last6=Bordachar|first6=Pierre|last7=Boriani|first7=Giuseppe|last8=Breithardt|first8=Ole-A.|last9=Cleland|first9=John|date=August 2013|title=2013 ESC guidelines on cardiac pacing and cardiac resynchronization therapy: the task force on cardiac pacing and resynchronization therapy of the European Society of Cardiology (ESC). Developed in collaboration with the European Heart Rhythm Association (EHRA)|journal=Europace|volume=15|issue=8|pages=1070–1118|doi=10.1093/europace/eut206|issn=1532-2092|pmid=23801827|doi-access=free|hdl=11380/1080452|hdl-access=free}}</ref> Implantable defibrillators are used to treat serious life-threatening rapid heart rhythms. These devices monitor the heart, and if dangerous heart racing is detected can automatically deliver a shock to restore the heart to a normal rhythm. Implantable defibrillators are most commonly used in patients with heart failure, [[Cardiomyopathy|cardiomyopathies]], or inherited arrhythmia syndromes.

==== Heart failure ====
{{Main|Heart failure}}As well as addressing the underlying cause for a patient's heart failure (most commonly [[Coronary artery disease|ischemic heart disease]] or [[hypertension]]), the mainstay of heart failure treatment is with medication. These include drugs to prevent fluid from accumulating in the lungs by increasing the amount of urine a patient produces ([[diuretic]]s), and drugs that attempt to preserve the pumping function of the heart ([[beta blocker]]s, [[ACE inhibitor]]s and [[Antimineralocorticoid|mineralocorticoid receptor antagonists]]).<ref name=":2">{{Cite journal|last1=Ponikowski|first1=Piotr|last2=Voors|first2=Adriaan A.|last3=Anker|first3=Stefan D.|last4=Bueno|first4=Héctor|last5=Cleland|first5=John G.F.|last6=Coats|first6=Andrew J.S.|last7=Falk|first7=Volkmar|last8=González-Juanatey|first8=José Ramón|last9=Harjola|first9=Veli-Pekka|date=August 2016|title=2016 ESC Guidelines for the diagnosis and treatment of acute and chronic heart failure: The Task Force for the diagnosis and treatment of acute and chronic heart failure of the European Society of Cardiology (ESC). Developed with the special contribution of the Heart Failure Association (HFA) of the ESC|journal=European Journal of Heart Failure|volume=18|issue=8|pages=891–975|doi=10.1002/ejhf.592|issn=1879-0844|pmid=27207191|hdl=2434/427148|s2cid=221675744|url=https://orbi.uliege.be/bitstream/2268/205777/1/2016%20ESC%20Guidelines%20for%20the%20diagnosis%20and%20treatment%20of%20acute%20and%20chronic%20heart%20failure.pdf|access-date=24 September 2019|archive-date=14 June 2020|archive-url=https://web.archive.org/web/20200614214934/https://orbi.uliege.be/bitstream/2268/205777/1/2016%20ESC%20Guidelines%20for%20the%20diagnosis%20and%20treatment%20of%20acute%20and%20chronic%20heart%20failure.pdf|url-status=live}}</ref>

In some patients with heart failure, a specialised pacemaker known as [[Cardiac resynchronization therapy|cardiac resynchronisation therapy]] can be used to improve the heart's pumping efficiency.<ref name=":1" /> These devices are frequently combined with a defibrillator. In very severe cases of heart failure, a small pump called a [[ventricular assist device]] may be implanted which supplements the heart's own pumping ability. In the most severe cases, a [[Heart transplantation|cardiac transplant]] may be considered.<ref name=":2" />

== History ==
=== Ancient ===
[[File:Leonardo da vinci, Heart and its Blood Vessels.jpg|thumb|Heart and its blood vessels, by [[Leonardo da Vinci]], 15th century]]
Humans have known about the heart since ancient times, although its precise function and anatomy were not clearly understood.<ref name="USYD2016">{{cite web|title=Anatomy of the Heart|url=https://sydney.edu.au/medicine/museum/mwmuseum/index.php/Anatomy_of_the_Heart|website=University of Sydney Online Museum|access-date=2 August 2016|url-status=live|archive-url=https://web.archive.org/web/20160818202606/https://sydney.edu.au/medicine/museum/mwmuseum/index.php/Anatomy_of_the_Heart|archive-date=18 August 2016}}</ref> From the primarily religious views of earlier societies towards the heart, [[ancient Greece|ancient Greeks]] are considered to have been the primary seat of scientific understanding of the heart in the ancient world.<ref name="Anaemia2010">{{cite journal|last1=Meletis|first1=John|last2=Konstantopoulos|first2=Kostas|title=The Beliefs, Myths, and Reality Surrounding the Word Hema (Blood) from Homer to the Present|journal=Anemia|date=2010|volume=2010|article-number=857657|doi=10.1155/2010/857657|pmid=21490910|pmc=3065807|doi-access=free}}</ref><ref name="Katz2008">{{cite journal|last1=Katz|first1=A. M.|title=The 'Modern' View of Heart Failure: How Did We Get Here?|journal=Circulation: Heart Failure|date=1 May 2008|volume=1|issue=1|pages=63–71|doi=10.1161/CIRCHEARTFAILURE.108.772756|pmid=19808272|doi-access=free}}</ref><ref name="Aird2011">{{cite journal|last1=Aird|first1=W.C.|title=Discovery of the cardiovascular system: from Galen to William Harvey|journal=Journal of Thrombosis and Haemostasis|date=July 2011|volume=9|pages=118–129|doi=10.1111/j.1538-7836.2011.04312.x|pmid=21781247|s2cid=12092592|doi-access=free}}</ref> [[Aristotle]] considered the heart to be the organ responsible for creating blood; [[Plato]] considered the heart as the source of circulating blood and [[Hippocrates]] noted blood circulating cyclically from the body through the heart to the lungs.<ref name=Anaemia2010 /><ref name=Aird2011 /> [[Erasistratos]] (304–250 BCE) noted the heart as a pump, causing dilation of blood vessels, and noted that arteries and veins both radiate from the heart, becoming progressively smaller with distance, although he believed they were filled with air and not blood. He also discovered the heart valves.<ref name=Anaemia2010 />

The Greek physician [[Galen]] (2nd century CE) knew blood vessels carried blood and identified venous (dark red) and arterial (brighter and thinner) blood, each with distinct and separate functions.<ref name=Anaemia2010 /> Galen, noting the heart as the hottest organ in the body, concluded that it provided heat to the body.<ref name=Aird2011 /> The heart did not pump blood around, the heart's motion sucked blood in during diastole and the blood moved by the pulsation of the arteries themselves.<ref name=Aird2011 /> Galen believed the arterial blood was created by venous blood passing from the left ventricle to the right through 'pores' between the ventricles.<ref name=USYD2016 /> Air from the lungs passed from the lungs via the pulmonary artery to the left side of the heart and created arterial blood.<ref name=Aird2011/>

These ideas went unchallenged for almost a thousand years.<ref name=USYD2016 /><ref name=Aird2011/>

=== Pre-modern ===
The earliest descriptions of the [[coronary circulation|coronary]] and pulmonary circulation systems can be found in the ''[[Commentary on Anatomy in Avicenna's Canon]]'', published in 1242 by [[Ibn al-Nafis]].<ref name="Michelakis">{{cite journal|last1=Michelakis|first1=E.D.|title=Pulmonary Arterial Hypertension: Yesterday, Today, Tomorrow|journal=[[Circulation Research]]|date=19 June 2014|volume=115|issue=1|pages=109–114|doi=10.1161/CIRCRESAHA.115.301132|pmid=24951761|doi-access=free}}</ref> In his manuscript, al-Nafis wrote that blood passes through the pulmonary circulation instead of moving from the right to the left ventricle as previously believed by Galen.<ref name="West2008">{{cite journal|last=West|first=John|title=Ibn al-Nafis, the pulmonary circulation, and the Islamic Golden Age|journal=[[Journal of Applied Physiology]]|year=2008|doi=10.1152/japplphysiol.91171.2008|volume=105|issue=6|pmid=18845773|pmc=2612469|pages=1877–1880}}</ref> His work was later translated into [[Latin]] by [[Andrea Alpago]].<ref>{{cite journal|last1=Bondke Persson|first1=A.|last2=Persson|first2=P.B.|title=Form and function in the vascular system|journal=[[Acta Physiologica]]|volume=211|issue=3|pages=468–470|doi=10.1111/apha.12309|pmid=24800879|year=2014|s2cid=26211642}}</ref>

In Europe, the teachings of Galen continued to dominate the academic community and his doctrines were adopted as the official canon of the Church. [[Andreas Vesalius]] questioned some of Galen's beliefs of the heart in ''[[De humani corporis fabrica]]'' (1543), but his [[Masterpiece|magnum opus]] was interpreted as a challenge to the authorities and he was subjected to a number of attacks.<ref name="west2014">{{cite journal|last1=West|first1=J.B.|title=Galen and the beginnings of Western physiology|journal=[[American Journal of Physiology|AJP: Lung Cellular and Molecular Physiology]]|date=30 May 2014|volume=307|issue=2|pages=L121–L128|doi=10.1152/ajplung.00123.2014|pmid=24879053|s2cid=5656712|url=http://pdfs.semanticscholar.org/bd6b/3bb1b19195825c9a5ac2c1201ddc5925aa6b.pdf|archive-url=https://web.archive.org/web/20190302220754/http://pdfs.semanticscholar.org/bd6b/3bb1b19195825c9a5ac2c1201ddc5925aa6b.pdf|archive-date=2 March 2019}}</ref> [[Michael Servetus]] wrote in ''[[Christianismi Restitutio]]'' (1553) that blood flows from one side of the heart to the other via the lungs.<ref name="west2014"/>

=== Modern ===
[[File:Animated Heart - Old Textbook style.gif|thumb|Animated heart]]

A breakthrough in understanding the flow of blood through the heart and body came with the publication of ''[[Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus|De Motu Cordis]]'' (1628) by the English physician [[William Harvey]]. Harvey's book completely describes the systemic circulation and the mechanical force of the heart, leading to an overhaul of the Galenic doctrines.<ref name="Aird2011"/> [[Otto Frank (physiologist)|Otto Frank]] (1865–1944) was a German physiologist; among his many published works are detailed studies of this important heart relationship. [[Ernest Starling]] (1866–1927) was an important English physiologist who also studied the heart. Although they worked largely independently, their combined efforts and similar conclusions have been recognized in the name "[[Frank–Starling mechanism]]".<ref name="CNX2014"/>

Although [[Purkinje fibers]] and the [[bundle of His]] were discovered as early as the 19th century, their specific role in the [[electrical conduction system of the heart]] remained unknown until [[Sunao Tawara]] published his monograph, titled ''[[Das Reizleitungssystem des Säugetierherzens]]'', in 1906. Tawara's discovery of the [[atrioventricular node]] prompted [[Arthur Keith]] and [[Martin Flack]] to look for similar structures in the heart, leading to their discovery of the [[sinoatrial node]] several months later. These structures form the anatomical basis of the electrocardiogram, whose inventor, [[Willem Einthoven]], was awarded the Nobel Prize in Medicine or Physiology in 1924.<ref>{{cite journal|last1=Silverman|first1=M.E.|title=Why Does the Heart Beat?: The Discovery of the Electrical System of the Heart|journal=[[Circulation (journal)|Circulation]]|date=13 June 2006|volume=113|issue=23|pages=2775–2781|doi=10.1161/CIRCULATIONAHA.106.616771|pmid=16769927|doi-access=free}}</ref>

The first [[Heart transplantation|heart transplant]] in a human ever performed was by [[James Hardy (surgeon)|James Hardy]] in 1964, using a chimpanzee heart, but the patient died within 2 hours.<ref>{{Cite journal |last=Cooper |first=David K.C. |date=2012-01-01 |title=A Brief History of Cross-Species Organ Transplantation |journal=Baylor University Medical Center Proceedings |volume=25 |issue=1 |pages=49–57 |doi=10.1080/08998280.2012.11928783 |issn=0899-8280 |pmc=3246856 |pmid=22275786}}</ref> The first human to human heart transplantation was performed in 1967 by the South African surgeon [[Christiaan Barnard]] at [[Groote Schuur Hospital]] in [[Cape Town]].<ref>{{Cite news |date=2017-12-03 |title=The operation that took medicine into the media age |language=en-GB |work=BBC News |url=https://www.bbc.com/news/health-42170023 |access-date=2022-06-09}}</ref><ref>{{Cite book |title=Organ Donation |publisher=Greenhaven Publishing LLC |year=2012 |isbn=978-0-7377-6269-3 |page=18}}</ref> This marked an important milestone in [[cardiac surgery]], capturing the attention of both the medical profession and the world at large. However, long-term survival rates of patients were initially very low. [[Louis Washkansky]], the first recipient of a donated heart, died 18 days after the operation while other patients did not survive for more than a few weeks.<ref>{{cite journal|last1=Cooley|first1=Denton A.|title=Recollections of the Early Years of Heart Transplantation and the Total Artificial Heart|journal=Artificial Organs|volume=35|issue=4|pages=353–357|doi=10.1111/j.1525-1594.2011.01235.x|pmid=21501184|year=2011|doi-access=free}}</ref> The American surgeon [[Norman Shumway]] has been credited for his efforts to improve transplantation techniques, along with pioneers [[Richard Lower (surgeon)|Richard Lower]], [[Vladimir Demikhov]] and [[Adrian Kantrowitz]]. As of March 2000, more than 55,000 heart transplantations have been performed worldwide.<ref>{{cite journal|last1=Miniati|first1=Douglas N.|last2=Robbins|first2=Robert C.|title=Heart transplantation: a thirty-year perspective: A Thirty-Year Perspective|journal=[[Annual Review of Medicine]]|volume=53|issue=1|pages=189–205|doi=10.1146/annurev.med.53.082901.104050|pmid=11818470|year=2002}}</ref> The first successful transplant of a heart from a [[Genetically modified organism|genetically modified]] pig to a human in which the patient lived for a longer time, was performed January 7, 2022 in [[Baltimore]] by heart surgeon [[Bartley P. Griffith]], recipient was David Bennett (57) this successfully extended his life until 8 March 2022 (1 month and 30 days).<ref>{{Cite web |title=2022 News – In Memoriam: David Bennett, Sr. {{!}} University of Maryland School of Medicine |url=https://www.medschool.umaryland.edu/news/2022/IN-MEMORIAM-David-Bennett-Sr.html |access-date=2022-06-09 |website=www.medschool.umaryland.edu}}</ref>

By the middle of the 20th century, [[Cardiovascular disease|heart disease]] had surpassed infectious disease as the leading cause of death in the United States, and it is currently the leading cause of deaths worldwide. Since 1948, the ongoing [[Framingham Heart Study]] has shed light on the effects of various influences on the heart, including diet, exercise, and common medications such as aspirin. Although the introduction of [[ACE inhibitor]]s and [[beta blocker]]s has improved the management of chronic heart failure, the disease continues to be an enormous medical and societal burden, with 30 to 40% of patients dying within a year of receiving the diagnosis.<ref>{{cite journal|last1=Neubauer|first1=Stefan|s2cid=1481349|title=The Failing Heart – An Engine Out of Fuel|journal=[[New England Journal of Medicine]]|date=15 March 2007|volume=356|issue=11|pages=1140–1151|doi=10.1056/NEJMra063052|pmid=17360992}}</ref>

==Society and culture==
{{further|Sacred Heart|Heart symbol|Blood#Cultural and religious beliefs}}
{{Hiero|''jb'' (F34) "heart"|<hiero>F34</hiero>|align=right|era=egypt}}
===Symbolism===
{{multiple image
| align = right
| direction =
| width =
| image1 = Heart corazón.svg
| width1 = 100
| caption1 = Common [[Heart (symbol)|heart symbol]]
| image2 = Гхани.png
| width2 = 100
| caption2 =Letter [[wikt:ღ|ღ]] of the [[Georgian script]] is often used as a "heart" symbol.
| image3 = 心-bigseal.svg
| width3 = 100
| caption3 = The [[seal script]] glyph for "heart" ([[Middle Chinese]] ''sim'')
}}
[[File:Amaranthe - Wacken Open Air 2018-2480.jpg|thumb|right|[[Elize Ryd]] making a heart sign at a concert in 2018]]
[[File:Emma Myers 2025 (2).png|thumb|American actress [[Emma Myers]] making a heart sign at a [[Wednesday (TV series)|Wednesday]] promotional event in 2025]]
As one of the vital organs, the heart was long identified as the center of the entire body, the seat of life, or emotion, or reason, will, intellect, purpose or the mind.<ref name=WATKINS>{{cite book|title=The Watkins Dictionary of Symbols|isbn=978-1-78028-357-9|chapter=Heart|last1=Tresidder|first1=Jack|year=2012|publisher=Watkins Media Limited }}</ref> The heart is an emblematic symbol in many religions, signifying "truth, conscience or moral courage in many religions—the temple or throne of God in Islamic and [[Judeo-Christian]] thought; the divine centre, or [[Ātman (Hinduism)|atman]], and the [[third eye]] of transcendent wisdom in [[Hinduism]]; the diamond of purity and essence of the [[Buddha]]; the [[Taoism|Taoist]] centre of understanding."<ref name=WATKINS />

In the [[Hebrew Bible]], the word for heart, ''lev'', is used in these meanings, as the seat of emotion, the mind, and referring to the anatomical organ. It is also connected in function and symbolism to the stomach.<ref>{{cite book|last1=Rosner|first1=Fred|title=Medicine in the Bible and the Talmud: selections from classical Jewish sources|date=1995|publisher=KTAV Pub. House|location=Hoboken, NJ|isbn=978-0-88125-506-5|pages=87–96|edition=Augm.}}</ref>

An important part of the concept of the [[Egyptian soul|soul]] in [[Ancient Egyptian religion]] was thought to be the heart, or ''ib''. The ''ib'' or metaphysical heart was believed to be formed from one drop of blood from the child's mother's heart, taken at conception.<ref>[https://www.britannica.com/EBchecked/topic/280503/ib ''Britannica'', ''Ib''] {{webarchive|url=https://web.archive.org/web/20090107185547/https://www.britannica.com./EBchecked/topic/280503/ib |date=7 January 2009 }}. The word was also transcribed by [[E. A. Wallis Budge|Wallis Budge]] as ''Ab.''</ref> To ancient Egyptians, the heart was the seat of [[emotion]], [[thought]], will, and [[intention]]. This is evidenced by [[Egyptian language|Egyptian]] expressions which incorporate the word ''ib'', such as ''Awi-ib'' for "happy" (literally, "long of heart"), ''Xak-ib'' for "estranged" (literally, "truncated of heart").<ref>{{cite book|last1=Allen|first1=James P.|title=Middle Egyptian: an introduction to the language and culture of hieroglyphs|date=2014|isbn=978-1-107-66328-2|pages=453, 465|publisher=Cambridge University Press |edition=3rd}}</ref> In Egyptian religion, the heart was the key to the afterlife. It was conceived as surviving death in the nether world, where it gave evidence for, or against, its possessor. The heart was therefore not removed from the body during mummification, and was believed to be the center of intelligence and feeling, and needed in the afterlife.<ref>{{Cite web |title=Mummification |url=http://www.ancientegypt.co.uk/mummies/story/page3.html |access-date=2022-12-20 |website=www.ancientegypt.co.uk}}</ref> It was thought that the heart was examined by [[Anubis]] and a variety of [[ancient Egyptian deities|deities]] during the ''Weighing of the Heart'' ceremony. If the heart weighed more than the feather of [[Maat]], which symbolized the ideal standard of behavior. If the scales balanced, it meant the heart's possessor had lived a just life and could enter the afterlife; if the heart was heavier, it would be devoured by the monster [[Ammit]].<ref>{{cite book|last1=Taylor|first1=John H.|title=Death and the afterlife in ancient Egypt|date=2001|publisher=The University of Chicago Press|location=Chicago|isbn=978-0-226-79164-7|pages=35–38}}</ref>

The [[Chinese language|Chinese]] character for "heart", 心, derives from a comparatively realistic depiction of a heart (indicating the heart chambers) in [[seal script]].<ref>{{cite book|first1=Qiu |last1=Xigui |first2=Gilbert L |last2= Mattos|title=Chinese writing = Wenzi-xue-gaiyao|date=2000|publisher=Society for the Study of Early China [u.a.]|location=Berkeley|isbn=978-1-55729-071-7|page=176}}</ref> The Chinese word [[:wikt:心#Mandarin|''xīn'']] also takes the metaphorical meanings of "mind", "intention", or "core", and is often translated as "heart-mind" as the ancient Chinese believed the heart was the center of human cognition.<ref>MDBG online dictionary. [http://www.mdbg.net/chindict/chindict.php?page=worddict&wdrst=0&wdqb=%E5%BF%83 "心"] {{webarchive|url=https://web.archive.org/web/20161004224839/http://www.mdbg.net/chindict/chindict.php?page=worddict&wdrst=0&wdqb=%E5%BF%83 |date=4 October 2016 }}.</ref> [[Heart (Chinese medicine)|In Chinese medicine]], the heart is seen as the center of [[Shen (Chinese religion)|神 ''shén'']] "spirit, consciousness".<ref>{{cite book|last1=Rogers|first1=Flaws, Bob|title=Statements of fact in traditional Chinese medicine|date=2007|publisher=Blue Poppy Press|location=Boulder, Colo.|isbn=978-0-936185-52-1|edition=3rd|page=47|url=https://books.google.com/books?id=tKNrg-gG3pgC&pg=PA47|access-date=16 August 2020|archive-date=14 April 2021|archive-url=https://web.archive.org/web/20210414025301/https://books.google.com/books?id=tKNrg-gG3pgC&pg=PA47|url-status=live}}</ref> The heart is associated with the [[small intestine]], [[tongue]], governs the [[Zang-fu|six organs and five viscera]], and belongs to fire in the five elements.<ref>{{cite book|last1=Wiseman|first1=Nigel|last2=Ye|first2=Feng|title=A practical dictionary of Chinese medicine|date=1998|publisher=Paradigm Publications|location=Brookline, MA|isbn=978-0-912111-54-4|edition=1st|page=260}}</ref>

The Sanskrit word for heart is ''hṛd'' or ''hṛdaya'', found in the oldest surviving Sanskrit text, the [[Rigveda]]. In Sanskrit, it may mean both the anatomical object and "mind" or "soul", representing the seat of emotion. ''Hrd'' may be a cognate of the word for heart in Greek, Latin, and English.<ref>{{citation|author=Sellmer, Sven|editor1=Piotr Balcerowicz|editor2=Marek Mejor|title=Essays in Indian Philosophy, Religion and Literature|chapter-url=https://books.google.com/books?id=b2qPLswTCSIC&pg=PA71|year=2004|publisher=Motilal Banarsidass Publishers|location=Delhi|isbn=978-81-208-1978-8|pages=71–83|chapter=The Heart in the ''Ŗg veda''|url-status=live|archive-url=https://web.archive.org/web/20161206085205/https://books.google.com/books?id=b2qPLswTCSIC&pg=PA71|archive-date=6 December 2016}}</ref><ref>{{cite book|last1=Lanman|first1=Charles Rockwell|title=A Sanskrit reader: text and vocabulary and notes|date=1996|publisher=Motilal Banarsidass|location=Delhi|isbn=978-81-208-1363-2|page=287|edition=repr}}</ref>

Many [[classical antiquity|classical]] philosophers and scientists, including [[Aristotle]], considered the heart the seat of thought, [[reason]], or emotion, often disregarding the brain as contributing to those functions.<ref>{{cite book |title=On the Parts of Animals |author=Aristotle |author-link=Aristotle |url=http://ebooks.adelaide.edu.au/a/aristotle/parts/book3.html|page=book 3, ch. 4 |no-pp=y |archive-url=https://web.archive.org/web/20160814220201/https://ebooks.adelaide.edu.au/a/aristotle/parts/book3.html |archive-date=14 August 2016}} ([[De Partibus Animalium|De partibus animalium]])</ref> The identification of the heart as the seat of [[emotion]]s in particular is due to the [[Roman Empire|Roman]] physician [[Galen]], who also located the seat of the passions in the [[liver]], and the seat of reason in the brain.<ref>[[Galen]], ''De usu partium corporis humani'' ("The Use of the Parts of the Human Body"), book 6.</ref>

The heart also played a role in the [[Aztec]] system of belief. The most common form of human sacrifice practiced by the Aztecs was heart-extraction. The Aztec believed that the heart (''tona'') was both the seat of the individual and a fragment of the Sun's heat (''istli''). To this day, the Nahua consider the Sun to be a heart-soul (''tona-tiuh''): "round, hot, pulsating".<ref>Sandstrom, Alan (1991) ''Corn is Our Blood''. University of Oklahoma Press. pp. 239–240. {{ISBN|0-8061-2403-2}}.</ref>

Indigenous leaders from Alaska to Australia came together in 2020 to deliver a message to the world that humanity needs to shift from the mind to the heart, and let our heart be in charge of what we do.<ref name=":5">{{Cite news |date=2020-04-20 |title='Listen to your heart': Indigenous elders channel tough love in Earth Day film |language=en |work=Reuters |url=https://www.reuters.com/article/us-earth-day-indigenous-idCAKBN2221G7 |access-date=2022-12-20}}</ref> The message was made into a film, which highlighted that humanity must open their hearts to restore balance to the world.<ref>{{Cite web |title=Prophecy  |url=https://www.wisdomweavers.world/prophecy |access-date=2022-12-20 |website=Wisdom Weavers of the World  |language=en-US}}</ref> Kumu Sabra Kauka, a Hawaiian studies educator and tradition bearer summed up the message of the film saying "Listen to your heart. Follow your path. May it be clear, and for the good of all."<ref name=":5" />  The film was led by Illarion Merculieff from the [[Aleut]] (Unangan) tribe. Merculieff has written that Unangan Elders referred to the heart as a "source of wisdom", "a deeper portal of profound interconnectedness and awareness that exists between humans and all living things".<ref>{{Cite web |last=Nature |first=Center for Humans and |date=2017-06-16 |title=Out of the Head, Into the Heart: The Way of the Human Being |url=https://humansandnature.org/out-of-the-head-into-the-heart-the-way-of-the-human-being/ |access-date=2022-12-20 |website=Center for Humans and Nature |language=en-US}}</ref><ref>{{Cite web |last=Bioneers |date=2019-03-22 |title=The Indigenous Art of Following Wisdom from the Heart |url=https://bioneers.org/the-indigenous-art-of-following-wisdom-from-the-heart-ze0z1903/ |access-date=2022-12-20 |website=Bioneers |language=en-US}}</ref>

In [[Catholicism]], there has been a long tradition of veneration of the heart, stemming from worship of the wounds of [[Jesus Christ]] which gained prominence from the mid sixteenth century.<ref>{{cite book|vauthors = Kurian G|title=Nelson's Dictionary of Christianity: The Authoritative Resource on the Christian World|date=2001|publisher=Thomas Nelson Inc.|isbn=978-1-4185-3981-8|chapter=Sacred Heart of Jesus}}</ref> This tradition influenced the development of the medieval Christian [[Catholic devotions|devotion]] to the [[Sacred Heart of Jesus]] and the parallel veneration of the [[Immaculate Heart of Mary]], made popular by [[John Eudes]].<ref>{{cite book|last1=Murray|first1=Tom Devonshire Jones; Linda Murray; Peter|title=The Oxford dictionary of christian art and architecture|date=2013|publisher=Oxford University Press|location=Corby|isbn=978-0-19-968027-6|chapter=Heart|edition=2nd}}</ref> There are also many references to the heart in the Christian Bible, including "Blessed are the pure in heart, for they will see God",<ref>{{Cite web |title=Bible Gateway passage: Matthew 5:8 – New International Version |url=https://www.biblegateway.com/passage/?search=Matthew%205%3A8&version=NIV |access-date=2022-12-19 |website=Bible Gateway |language=en}}</ref> "Above all else, guard your heart, for everything you do flows from it",<ref>{{Cite web |title=Bible Gateway passage: Proverbs 4:23 – New International Version |url=https://www.biblegateway.com/passage/?search=Proverbs%204%3A23&version=NIV |access-date=2022-12-19 |website=Bible Gateway |language=en}}</ref> "For where your treasure is, there your heart will be also",<ref>{{Cite web |title=Bible Gateway passage: Matthew 6:21 – New International Version |url=https://www.biblegateway.com/passage/?search=Matthew%206%3A21&version=NIV |access-date=2022-12-22 |website=Bible Gateway |language=en}}</ref> "For as a man thinks in his heart, so shall he be."<ref>{{Cite web |title=Bible Gateway passage: Proverbs 23:7 – New King James Version |url=https://www.biblegateway.com/passage/?search=Proverbs%2023%3A7&version=NKJV |access-date=2022-12-19 |website=Bible Gateway |language=en}}</ref>

The expression of a [[broken heart]] is a cross-cultural reference to [[grief]] for a lost one or to unfulfilled [[romantic love]].

The notion of "[[Cupid]]'s arrows" is ancient, due to [[Ovid]], but while Ovid describes Cupid as wounding his victims with his arrows, it is not made explicit that it is the ''heart'' that is wounded. The familiar iconography of Cupid shooting little [[heart shape|heart symbols]] is a [[Renaissance]] theme that became tied to [[Valentine's Day]].<ref name=WATKINS />

In certain [[Trans–New Guinea languages|Trans-New Guinea languages]], such as [[Foi language|Foi]] and Momoona, the heart and seat of emotions are [[Colexification|colexified]], meaning they share the same word.<ref>{{Cite book |last1=Pawley |first1=Andrew |title=The Trans New Guinea family |last2=Hammarström |first2=Harald |page=125}}</ref>

===Cuisine===
{{anchor|Food|Heart as food}}
Animal hearts are widely consumed as a type of [[offal]]. As they are almost entirely muscle, they are high in protein. They are often included in dishes with other internal organs, for example in the [[Ottoman cuisine|pan-Ottoman]] [[kokoretsi]].

[[Chicken (food)|Chicken]] hearts are considered to be [[giblets]], and are often grilled on skewers; examples of this are [[Japanese cuisine|Japanese]] [[yakitori|''hāto yakitori'']], [[Brazilian cuisine|Brazilian]] [[churrasco|''churrasco de coração'']], and [[Indonesian cuisine|Indonesian]] [[satay|chicken heart satay]].<ref>''Indonesia Magazine'', '''25''' (1994), p. 67</ref> They can also be pan-fried, as in [[Jerusalem mixed grill]]. In [[Egyptian cuisine]], they can be used, finely chopped, as part of [[stuffing]] for chicken.<ref>Abdennour, Samia (2010) "Firakh mahshiya wi mihammara", recipe 117, ''Egyptian Cooking: And Other Middle Eastern Recipes'', American University in Cairo Press. {{ISBN|977-424-926-7}}.</ref> Many recipes combined them with other giblets, such as the [[Mexican cuisine|Mexican]] ''pollo en menudencias''<ref>[[Diana Kennedy|Kennedy, Diana]] (2013) ''My Mexico: A Culinary Odyssey with Recipes'', University of Texas Press. p. 100. {{ISBN|0-292-74840-X}}.</ref> and the [[Russian cuisine|Russian]] ''ragu iz kurinyikh potrokhov''.<ref>Sacharow, Alla (1993) ''Classic Russian Cuisine: A Magnificent Selection of More Than 400 Traditional Recipes''. {{ISBN|1-55970-174-9}}</ref>

The hearts of beef, pork, and mutton can generally be interchanged in recipes.{{citation needed|date=November 2024}} As heart is a hard-working muscle, it makes for "firm and rather dry" meat,<ref>{{cite book|first1=Irma S.|last1=Rombauer|author-link=Irma S. Rombauer|first2=Marion Rombauer|last2=Becker|first3=Ethan|last3=Becker|isbn=978-0-02-604570-4|publisher=The Bobbs-Merrill Company|title=The Joy of Cooking|year=1975|page=[https://archive.org/details/joyofcooking400romb/page/508 508]|url-access=registration|url=https://archive.org/details/joyofcooking400romb}}</ref> so is generally slow-cooked. Another way of dealing with toughness is to [[Julienning|julienne]] the meat, as in [[Chinese cuisine|Chinese]] stir-fried heart.<ref>Schwabe, Calvin W. (1979) ''Unmentionable Cuisine'', University of Virginia Press, {{ISBN|0-8139-1162-1}}, p. 96</ref>

[[Beef]] heart is valued for its high meat quality and low price, being commonly disregarded in conventional meat pricing. It can be cut into [[steaks]], comparable in quality to the more expensive cuts of meat from the same animal, though it is distinguished by a lack of a discernible grain. It was historically eaten in the United States as a cost-saving measure, but is today also eaten as an independently desirable ingredient.<ref>Gray, Melissa. [https://www.npr.org/sections/thesalt/2012/10/25/163618582/beef-heart-an-unexpected-meal-that-spans-generations "Beef Heart: An Unexpected Meal That Spans Generations"], ''NPR'', 25 October 2012.</ref> Beef heart may be grilled or braised.<ref name="joy">[[Irma S. Rombauer|Rombauer, Irma S.]] and Rombauer Becker, Marion (1975) ''[[The Joy of Cooking]]'', p. 508</ref> In the [[Peruvian cuisine|Peruvian]] [[anticuchos|''anticuchos de corazón'']], barbecued beef hearts are grilled after being tenderized through long [[marination]] in a spice and vinegar mixture. An [[Australian cuisine|Australian]] recipe for "mock goose" is actually braised stuffed beef heart.<ref>Torode, John (2009) ''Beef: And Other Bovine Matters'', Taunton Press, {{ISBN|1-60085-126-6}}, p. 230</ref>

[[Pork]] heart can be stewed, poached, braised,<ref>Milsom, Jennie (2009) ''The Connoisseur's Guide to Meat''. Sterling Publishing Company. p. 171. {{ISBN|1-4027-7050-2}}</ref> or made into sausage. The [[Balinese cuisine|Balinese]] ''oret'' is a sort of [[blood sausage]] made with pig heart and blood. A [[French cuisine|French]] recipe for ''cœur de porc à l'orange'' is made of braised heart with an orange sauce.

==Other animals==
{{See also|Circulatory system}}

===Vertebrates===
The size of the heart varies among the different animal [[phylum|groups]], with hearts in [[vertebrate]]s ranging from those of the smallest mice (12&nbsp;mg) to the blue whale (600&nbsp;kg).<ref>{{cite journal|last1=Dobson|first1=Geoffrey P|title=On Being the Right Size: Heart Design, Mitochondrial Efficiency and Lifespan Potential|journal=Clinical and Experimental Pharmacology and Physiology|date=August 2003|volume=30|issue=8|pages=590–597|doi=10.1046/j.1440-1681.2003.03876.x|pmid=12890185|s2cid=41815414|doi-access=}}</ref> In vertebrates, the heart lies in the middle of the ventral part of the body, surrounded by a [[pericardium]].<ref name="Hyman1992">{{cite book|author=Hyman, L. Henrietta|title=Hyman's Comparative Vertebrate Anatomy|url=https://books.google.com/books?id=VKlWjdOkiMwC&pg=PA448|year=1992|publisher=University of Chicago Press|isbn=978-0-226-87013-7|pages=448–|url-status=live|archive-url=https://web.archive.org/web/20161206001900/https://books.google.com/books?id=VKlWjdOkiMwC&pg=PA448|archive-date=6 December 2016}}</ref> which in some fish may be connected to the [[peritoneum]].<ref>{{cite book|editor=Shuttleworth, Trevor J.|title=Physiology of Elasmobranch Fishes|date=1988|publisher=Springer Berlin Heidelberg|location=Berlin, Heidelberg|isbn=978-3-642-73336-9|page=3|url=https://books.google.com/books?id=4VLoCAAAQBAJ&pg=PA3|access-date=16 August 2020|archive-date=14 April 2021|archive-url=https://web.archive.org/web/20210414054657/https://books.google.com/books?id=4VLoCAAAQBAJ&pg=PA3|url-status=live}}</ref> In all vertebrates, the heart has an asymmetric orientation, almost always on the left side. According to one theory, this is caused by a [[axial twist theory|developmental axial twist]] in the early embryo.<ref name="Lussanet2012">{{cite journal | last1=de Lussanet|first1=Marc H.E. | last2=Osse|first2=Jan W.M. | year=2012 | title=An ancestral axial twist explains the contralateral forebrain and the optic chiasm in vertebrates | journal=Animal Biology | volume=62 | issue=2|pages=193–216 | doi=10.1163/157075611X617102 | arxiv=1003.1872|s2cid=7399128|issn = 1570-7555 }}</ref><ref name="lussanet2019">{{cite journal | last=de Lussanet|first=M.H.E. | doi=10.7717/peerj.7096 | journal=PeerJ | article-number=e7096 | title=Opposite asymmetries of face and trunk and of kissing and hugging, as predicted by the axial twist hypothesis | volume=7 | year=2019 | pmid=31211022 | pmc=6557252 | doi-access=free}}</ref>

The sinoatrial node is found in all [[amniote]]s but not in more primitive vertebrates. In these animals, the muscles of the heart are relatively continuous, and the sinus venosus coordinates the beat, which passes in a wave through the remaining chambers. Since the sinus venosus is incorporated into the right atrium in amniotes, it is likely [[homology (biology)|homologous]] with the SA node. In teleosts, with their vestigial sinus venosus, the main centre of coordination is, instead, in the atrium. The rate of heartbeat varies enormously between different species, ranging from around 20 beats per minute in [[codfish]] to around 600 in [[hummingbird]]s<ref name=VB /> and up to 1,200 bpm in the [[ruby-throated hummingbird]].<ref>{{cite book |first=June |last=Osborne |title=The Ruby-Throated Hummingbird |year=1998 |publisher=University of Texas Press |isbn=978-0-292-76047-9 |page=[https://archive.org/details/rubythroatedhumm0000osbo/page/14 14] |url=https://archive.org/details/rubythroatedhumm0000osbo/page/14 }}</ref>

===Double circulatory systems===
{{Further|Reptile#Circulation|Snake#Internal organs}}
[[File:Copy of Ap Bio 2.svg|thumb|A cross section of a three-chambered adult amphibian heart. Note the single ventricle. The purple regions represent areas where mixing of oxygenated and de-oxygenated blood occurs. {{ordered list |Pulmonary vein |Left atrium |Right atrium |Ventricle |Conus arteriosus |Sinus venosus}}]]
Adult [[amphibian]]s and most [[reptile]]s have a [[double circulatory system]], meaning a circulatory system divided into arterial and venous parts. However, the heart itself is not completely separated into two sides. Instead, it is separated into three chambers—two atria and one ventricle. Blood returning from both the systemic circulation and the lungs is returned, and blood is pumped simultaneously into the systemic circulation and the lungs. The double system allows blood to circulate to and from the lungs which deliver oxygenated blood directly to the heart.<ref name=GRIMM2015>{{Cite book|url=https://books.google.com/books?id=WG9uBwAAQBAJ|title=Veterinary Anesthesia and Analgesia|last1=Grimm|first1=Kurt A.|last2=Lamont|first2=Leigh A.|last3=Tranquilli|first3=William J.|last4=Greene|first4=Stephen A.|last5=Robertson|first5=Sheilah A.|page=418|year=2015|publisher=John Wiley & Sons|isbn=978-1-118-52620-0|language=en|url-status=live|archive-url=https://web.archive.org/web/20161206212053/https://books.google.com/books?id=WG9uBwAAQBAJ|archive-date=6 December 2016}}</ref>

In reptiles, other than [[snake]]s, the heart is usually situated around the middle of the thorax. In terrestrial and arboreal snakes, it is usually located nearer to the head; in aquatic species the heart is more centrally located.<ref name="Seymour"/> There is a heart with three chambers: two atria and one ventricle. The form and function of these hearts are different from mammalian hearts due to the fact that snakes have an elongated body, and thus are affected by different environmental factors. In particular, the snake's heart relative to the position in their body has been influenced greatly by gravity. Therefore, snakes that are larger in size tend to have a higher [[blood pressure]] due to gravitational change.<ref name="Seymour">{{cite journal|last1=Seymour|first1=Roger S.|year=1987|title=Scaling of Cardiovascular Physiology in Snakes|journal=Integrative and Comparative Biology|language=en|volume=27|issue=1|pages=97–109|doi=10.1093/icb/27.1.97|issn=1540-7063|doi-access=free}}</ref> The ventricle is incompletely separated into two-halves by a wall ([[:wikt:septum|septum]]), with a considerable gap near the pulmonary artery and aortic openings. In most reptilian species, there appears to be little, if any, mixing between the bloodstreams, so the aorta receives, essentially, only oxygenated blood.<ref name=VB /><ref name=GRIMM2015 /> The exception to this rule is [[crocodile]]s, which have a four-chambered heart.<ref name=COLVILLE2015>{{Cite book|url=https://books.google.com/books?id=9DMwBwAAQBAJ|title=Clinical Anatomy and Physiology for Veterinary Technicians|last1=Colville|first1=Thomas P.|last2=Bassert|first2=Joanna M.|page=547|year=2015|publisher=Elsevier Health Sciences|isbn=978-0-323-35620-6|language=en|url-status=live|archive-url=https://web.archive.org/web/20161206110844/https://books.google.com/books?id=9DMwBwAAQBAJ|archive-date=6 December 2016}}</ref>

In the heart of [[lungfish]], the septum extends partway into the ventricle. This allows for some degree of separation between the de-oxygenated bloodstream destined for the lungs and the oxygenated stream that is delivered to the rest of the body. The absence of such a division in living amphibian species may be partly due to the amount of respiration that occurs through the skin; thus, the blood returned to the heart through the venae cavae is already partially oxygenated. As a result, there may be less need for a finer division between the two bloodstreams than in lungfish or other [[tetrapod]]s. Nonetheless, in at least some species of amphibian, the spongy nature of the ventricle does seem to maintain more of a separation between the bloodstreams. Also, the original valves of the [[conus arteriosus]] have been replaced by a spiral valve that divides it into two parallel parts, thereby helping to keep the two bloodstreams separate.<ref name=VB />

=== Full division ===
[[Archosaur]]s ([[crocodilia]]ns and [[bird]]s) and [[mammal]]s show complete separation of the heart into two pumps for a total of four heart chambers; it is thought that the four-chambered heart of archosaurs evolved independently from that of mammals. In crocodilians, there is a small opening, the [[foramen of Panizza]], at the base of the arterial trunks and there is some degree of mixing between the blood in each side of the heart, during a dive underwater;<ref name=nonimportantshunt1>{{cite journal |last1=Crigg |first1=Gordon |last2=Johansen |first2=Kjell |s2cid=28733499 |year=1987 |title=Cardiovascular Dynamics in Crocodylus Porosus Breathing Air And During Voluntary Aerobic Dives |journal=Journal of Comparative Physiology B |volume=157 |issue=3 |pages=381–392 |doi=10.1007/BF00693365 |url=http://espace.library.uq.edu.au/view/UQ:9269/_Crocodylus_poro.pdf |access-date=20 February 2019 |archive-date=28 August 2021 |archive-url=https://web.archive.org/web/20210828102937/https://espace.library.uq.edu.au/data/UQ_9269/_Crocodylus_poro.pdf?Expires=1630146664&Key-Pair-Id=APKAJKNBJ4MJBJNC6NLQ&Signature=KyKofJBI4oqlJwIFGuf6sY5Y9iqjzCyhkCo7ZN0mWF1e2rird4irPgGfFpXZ-KA91HxOYNgUd2KPb9x4npGjFTRCcMBOU~DwZ9UZf~NZt4zJhhEbAzKghtgVGp6f1q9XSda~v0UEiKJMALjnOK0dIDAuYRjsrGq8JoCs7zDtamTncowHlU3UmtSKbXOdJH6OwFSjhv7pp7t-mNJT28Cfx8F9sV0W1NH~Fu5UyMJQlfodQC00jL-86iSEKMqUXO-86L6I5SFANGQVl7qSNNwO1yL~f6BzXVWS6jSbDlcJ3soZt-tQrL3VqYZfhFQEJuYbFif-ijW2A~cJML0SujYkrA__ |url-status=live }}</ref><ref name=nonimportantshunt2>{{cite journal |last1=Axelsson |first1=Michael |last2=Craig |first2=Franklin |last3=Löfman |first3=Carl |last4=Nilsson |first4=Stefan |last5=Crigg |first5=Gordon |year=1996 |title=Dynamic Anatomical Study of Cardiac Shunting in Crocodiles Using High-Resolution Angioscopy |journal=The Journal of Experimental Biology |volume=199 |issue=2 |pages=359–365 |doi=10.1242/jeb.199.2.359 |pmid=9317958 |url=http://jeb.biologists.org/content/199/2/359.full.pdf |access-date=3 July 2012 |url-status=live |archive-url=https://web.archive.org/web/20150303181815/http://jeb.biologists.org/content/199/2/359.full.pdf |archive-date=3 March 2015|doi-access=free |bibcode=1996JExpB.199..359A }}</ref> thus, only in birds and mammals are the two streams of blood—those to the pulmonary and systemic circulations—permanently kept entirely separate by a physical barrier.<ref name=VB>{{cite book |last1=Romer |first1=Alfred Sherwood |last2=Parsons |first2=Thomas S. |year=1977 |title=The Vertebrate Body |publisher=Holt-Saunders International |location= Philadelphia|pages= 437–442|isbn= 978-0-03-910284-5}}</ref>

===Fish===
{{Main|Fish anatomy#Heart}}
{{See also|Venous heart}}
[[File:Two chamber heart.svg|thumb|{{center|Blood flow through the fish heart: sinus venosus, atrium, ventricle, and outflow tract}}]]
The heart evolved no less than 380&nbsp;million years ago in [[fish]].<ref name="380m">{{Cite web |url=https://www.bbc.com/news/science-environment-62912225 |publisher=[[BBC News]] |date=2022-09-15 |access-date=2022-09-16 |last=Ghosh |first=Pallab |lang=en-GB |title=World's oldest heart found in prehistoric fish}}</ref> Fish have what is often described as a two-chambered heart,<ref name="Jurd2004">{{cite book|last=Jurd|first=Richard David|title=Instant Notes Animal Biology|url=https://books.google.com/books?id=i9YwWhkHOs4C&pg=PA134|year=2004|publisher=Garland Science|isbn=978-1-85996-325-8|page=134|url-status=live|archive-url=https://web.archive.org/web/20161206110614/https://books.google.com/books?id=i9YwWhkHOs4C&pg=PA134|archive-date=6 December 2016}}</ref> consisting of one atrium to receive blood and one ventricle to pump it.<ref name="Ostrander2000"/> However, the fish heart has entry and exit compartments that may be called chambers, so it is also sometimes described as three-chambered<ref name="Ostrander2000">{{cite book|last=Ostrander|first=Gary Kent|title=The Laboratory Fish|url=https://books.google.com/books?id=Hp4YSFiSD0IC&pg=PT154|year=2000|publisher=Elsevier|isbn=978-0-12-529650-2|pages=154–155|url-status=live|archive-url=https://web.archive.org/web/20161206074402/https://books.google.com/books?id=Hp4YSFiSD0IC&pg=PT154|archive-date=6 December 2016}}</ref> or four-chambered,<ref name=Farrell2011>{{cite book|editor=Farrell, Anthony P|others=Stevens, E Don; Cech, Jr., Joseph J; Richards, Jeffrey G|title=Encyclopedia of Fish Physiology: From Genome to Environment|url=https://books.google.com/books?id=3bsgS125KH0C&pg=PP2315|year=2011|publisher=Academic Press|isbn=978-0-08-092323-9|page=2315|url-status=live|archive-url=https://web.archive.org/web/20161206101409/https://books.google.com/books?id=3bsgS125KH0C&pg=PP2315|archive-date=6 December 2016}}</ref> depending on what is counted as a chamber. The atrium and ventricle are sometimes considered "true chambers", while the others are considered "accessory chambers".<ref name="Shukla">{{cite book|last=Shukla|first=J.P.|title=Fish & Fisheries|url=https://books.google.com/books?id=a05t8fWR2wIC&pg=PA155|publisher=Rastogi Publications|isbn=978-81-7133-800-9|pages=154–155|url-status=live|archive-url=https://web.archive.org/web/20161206134115/https://books.google.com/books?id=a05t8fWR2wIC&pg=PA155|archive-date=6 December 2016}}</ref>

Primitive fish have a four-chambered heart, but the chambers are arranged sequentially so that this primitive heart is quite unlike the four-chambered hearts of mammals and birds. The first chamber is the [[sinus venosus]], which collects deoxygenated blood from the body through the [[hepatic vein|hepatic]] and [[cardinal vein (disambiguation)|cardinal veins]]. From here, blood flows into the atrium and then to the powerful muscular ventricle where the main pumping action will take place. The fourth and final chamber is the [[conus arteriosus]], which contains several valves and sends blood to the ''ventral aorta''. The ventral aorta delivers blood to the gills where it is oxygenated and flows, through the [[descending aorta|dorsal aorta]], into the rest of the body. (In [[tetrapod]]s, the ventral aorta has divided in two; one half forms the [[ascending aorta]], while the other forms the pulmonary artery).<ref name=VB />

In the adult fish, the four chambers are not arranged in a straight row but instead form an S-shape, with the latter two chambers lying above the former two. This relatively simple pattern is found in [[cartilaginous fish]] and in the [[ray-finned fish]]. In [[teleost]]s, the conus arteriosus is very small and can more accurately be described as part of the aorta rather than of the heart proper. The conus arteriosus is not present in any [[amniote]]s, presumably having been absorbed into the ventricles over the course of evolution. Similarly, while the sinus venosus is present as a vestigial structure in some reptiles and birds, it is otherwise absorbed into the right atrium and is no longer distinguishable.<ref name=VB />

===Invertebrates===
[[File:Structural organization of the heart of the mosquito Anopheles gambiae - image.ppat.v08.i11.g001.png|thumb|The tube-like heart (green) of the mosquito ''[[Anopheles gambiae]]'' extends horizontally across the body, interlinked with the diamond-shaped [[insect wing#Muscles|wing muscles]] (also green) and surrounded by [[pericardium|pericardial cells]] (red). Blue depicts [[cell nuclei]].]]
[[File:Arthropod body struct 01.png|thumb|left|Basic [[arthropod]] body structure – heart shown in red]]
[[Arthropod]]s and most [[mollusk]]s have an open circulatory system. In this system, deoxygenated blood collects around the heart in cavities ([[:wikt:sinus|sinuses]]). This blood slowly permeates the heart through many small one-way channels. The heart then pumps the blood into the [[hemocoel]], a cavity between the organs. The heart in arthropods is typically a muscular tube that runs the length of the body, under the back and from the base of the head. Instead of blood the circulatory fluid is [[haemolymph]] which carries the most commonly used [[respiratory pigment]], copper-based [[haemocyanin]] as the oxygen transporter. Haemoglobin is only used by a few arthropods.<ref name=SOLOMON2010>{{Cite book|url=https://books.google.com/books?id=qdQ8AAAAQBAJ|title=Biology|last1=Solomon|first1=Eldra|last2=Berg|first2=Linda|last3=Martin|first3=Diana W.|year=2010|page=939|publisher=Cengage Learning|isbn=978-1-133-17032-7|language=en|url-status=live|archive-url=https://web.archive.org/web/20161206054642/https://books.google.com/books?id=qdQ8AAAAQBAJ|archive-date=6 December 2016}}</ref>
[[File:Cephalopod systemic heart.svg|thumb|left|Schematic of [[cephalopod]] heart]]
In some other invertebrates such as [[earthworm]]s, the circulatory system is not used to transport oxygen and so is much reduced, having no veins or arteries and consisting of two connected tubes. Oxygen travels by diffusion and there are five small muscular vessels that connect these vessels that contract at the front of the animals that can be thought of as "hearts".<ref name=SOLOMON2010/>

[[Cephalopod|Squids and other cephalopods]] have two "gill hearts" also known as [[branchial heart]]s, and one "systemic heart".<ref>Schipp, R., von Boletzky, S., Jakobs, P. et al. "A congenital malformation of the systemic heart complex in Sepia officinalis L. (Cephalopoda)". Helgoländer Meeresunters. 52, 29–40 (1998). {{doi|10.1007/BF02908733}}</ref> The branchial hearts have two atria and one ventricle each, and pump to the [[gill]]s, whereas the systemic heart pumps to the body.<ref>{{cite web|title=Meet our animals|url=https://nationalzoo.si.edu/Animals/Invertebrates/facts/cephalopods/default.cfm|website=Smithsonian National Zoological Park|access-date=14 August 2016|archive-url=https://web.archive.org/web/20160729081825/https://nationalzoo.si.edu/Animals/Invertebrates/Facts/cephalopods/default.cfm|archive-date=29 July 2016}}</ref><ref name="Prosser1991">{{cite book|vauthors=Ladd, Prosser C|title=Comparative Animal Physiology, Environmental and Metabolic Animal Physiology|url=https://books.google.com/books?id=7fQvbFlQBaQC&pg=PA537|year=1991|publisher=John Wiley & Sons|isbn=978-0-471-85767-9|pages=537–|url-status=live|archive-url=https://web.archive.org/web/20161206215610/https://books.google.com/books?id=7fQvbFlQBaQC&pg=PA537|archive-date=6 December 2016}}</ref>
{{clear}}

Only the [[chordates]] (including vertebrates) and the [[hemichordates]] have a central "heart", which is a vesicle formed from the thickening of the [[aorta]] and contracts to pump blood. This suggests a presence of it in the last [[deuterostome|common ancestor of these groups]] (may have been lost in the [[echinoderms]]).

== Additional images ==
<gallery widths=180>
File:Blausen 0451 Heart Anterior.png|The human heart viewed from the front
File:Blausen 0456 Heart Posterior.png|The human heart viewed from behind
File:Blausen 0260 CoronaryVessels Anterior.png|The [[coronary circulation]]
File:2008 Internal Anatomy of the HeartN.jpg|Frontal section of the human heart
File:Slide2aaaaaa.JPG|An anatomical specimen of the heart
File:Human Heart and Circulatory System.png|Heart illustration with circulatory system
File:Animated Heart.gif|Animated heart 3D model rendered in computer
</gallery>

==Notes==
{{Notelist|2}}

==References==
{{CNX A&P}}
{{Reflist}}

==Bibliography==
* {{cite book|last=Hall|first=John|title=Guyton and Hall Textbook of Medical Physiology|year=2011|publisher=Saunders/Elsevier|location=Philadelphia|isbn=978-1-4160-4574-8|edition=12th|url=https://archive.org/details/guyton-and-hall-textbook-of-medical-physiology-pdfdrive.com/|ref={{harvid|Guyton & Hall|2011}}}}
* {{cite book|last1=Longo|first1=Dan|last2=Fauci|first2=Anthony|last3=Kasper|first3=Dennis|last4=Hauser|first4=Stephen|last5=Jameson|first5=J.|last6=Loscalzo|first6=Joseph|title=Harrison's Principles of Internal Medicine|year=2011|publisher=McGraw-Hill Professional|isbn=978-0-07-174889-6|edition=18th|ref={{harvid|Harrison's|2011}}}}
* {{cite book|editor=Susan Standring |editor2=Neil R. Borley|title=Gray's anatomy: the anatomical basis of clinical practice|date=2008|publisher=Churchill Livingstone|location=London|isbn=978-0-8089-2371-8|edition=40th|ref={{harvid|Gray's Anatomy|2008}}|display-editors=etal}}
* {{cite book |editor=Nicki R. Colledge |editor2=Brian R. Walker |editor3=Stuart H. Ralston |title=Davidson's principles and practice of medicine |date=2010|publisher=Churchill Livingstone/Elsevier|location=Edinburgh|isbn=978-0-7020-3085-7|edition=21st |ref={{harvid|Davidson's|2010}}}}

==External links==
{{Sister project links|n=no}}
* [https://www.bbc.com/news/world-us-canada-59944889 Transplantation of pig heart to human. BBC, 11 Jan 2022.]
* [https://www.youtube.com/watch?v=NeuLxMXxR40 Heart surgeon Bartley P Griffith talks about the unique transplant of pig heart to human.]
* [https://web.archive.org/web/20070207102008/http://www.nhlbi.nih.gov/health/dci/Diseases/hhw/hhw_pumping.html What Is the Heart?] – NIH
* [http://www.vhlab.umn.edu/atlas/index.shtml Atlas of Human Cardiac Anatomy]
* [http://anatomyguy.com/middle-mediastinum-and-heart-review/ Dissection review of the anatomy of the Human Heart including vessels, internal and external features]
* [http://www.meddean.luc.edu/lumen/MedEd/GrossAnatomy/thorax0/heartdev/main_fra.html Prenatal human heart development]
* [http://www.biology-pages.info/A/AnimalHearts.html Animal hearts: fish, squid]
* [https://www.bbc.co.uk/programmes/p003c1bh The Heart], BBC Radio 4 interdisciplinary discussion with David Wootton, Fay Bound Alberti & Jonathan Sawday (''In Our Time'', 1 June 2006)
* {{Cite EB1911 |wstitle=Heart |volume=13 |pages=129–134 |short=1}}
* [https://humanbodypartsanatomy.com/heart-anatomy-parts-names-functions-diagram/Human Heart Anatomy] detailed guide for medical college students and medical professionals.

{{Heart anatomy}}
{{Cardiovascular physiology}}

{{Authority control}}

{{DEFAULTSORT:Human Heart}}
[[Category:Heart| ]]
[[Category:Cardiac anatomy]]
[[Category:Articles containing video clips]]
[[Category:Wikipedia medicine articles ready to translate]]
[[Category:Organs (anatomy)]]