Editing Heart (section)

===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
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| 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"/>