heart valve heart valve a heart valve is a one-way valve that allows blood to flow in one direction through the chambers of the heart. four valves are usually present in a mammalian heart and together they determine the pathway of blood flow through the heart. a heart valve opens or closes according to differential blood pressure on each side. heart valvevalves of the heart in motion, the front wall of the heart is removed in this image.detailssystemcardiovascularidentifiersmeshd006351fma7110anatomical terminologythe four valves in the mammalian heart are two atrioventricular valves separating the upper atria from the lower ventricles – the mitral valve in the left heart, and the tricuspid valve in the right heart. the other two valves are at the entrance to the arteries leaving the heart these are the semilunar valves – the aortic valve at the aorta, and the pulmonary valve at the pulmonary artery. the heart also has a coronary sinus valve, and an inferior vena cava valve, not discussed here. structure structure of the heart valves blood flow through the valves the heart valves and the chambers are lined with endocardium. heart valves separate the atria from the ventricles, or the ventricles from a blood vessel. heart valves are situated around the fibrous rings of the cardiac skeleton. the valves incorporate flaps called leaflets or cusps, similar to a duckbill valve or flutter valve, which are pushed open to allow blood flow and which then close together to seal and prevent backflow. the mitral valve has two cusps, whereas the others have three. there are nodules at the tips of the cusps that make the seal tighter. the pulmonary valve has left, right, and anterior cusps. the aortic valve has left, right, and posterior cusps. the tricuspid valve has anterior, posterior, and septal cusps; and the mitral valve has just anterior and posterior cusps. the valves of the human heart can be grouped in two sets: two atrioventricular valves to prevent backflow of blood from the ventricles into the atria: tricuspid valve or right atrioventricular valve, between the right atrium and right ventricle mitral valve or bicuspid valve, between the left atrium and left ventricle two semilunar valves to prevent the backflow of blood into the ventricle: pulmonary valve, located at the opening between the right ventricle and the pulmonary trunk aortic valve, located at the opening between the left ventricle and the aorta. valve number of flaps/cusps location prevent backflow of blood atrioventricular valves 3 (right), 2 (left) from the ventricles into the atria tricuspid valve 3 between the right atrium and right ventricle. bicuspid or mitral valve 2 between the left atrium and left ventricle. semilunar valves 3 (half-moon shaped) flaps into the ventricle pulmonary semilunar valve 3 (half-moon shaped) flaps at the opening between the right ventricle and the pulmonary trunk aortic semilunar valve 3 (half-moon shaped) flaps at the opening between the left ventricle and the aorta atrioventricular valves main articles: mitral valve and tricuspid valve 3d - loop of a heart viewed from the apex, with the apical part of the ventricles removed and the mitral valve clearly visible. due to missing data, the leaflets of the tricuspid and aortic valves are not clearly visible, but the openings are; the pulmonary valve is not visible. on the left are two standard 2d views (taken from the 3d dataset) showing tricuspid and mitral valves (above) and aortal valve (below). the atrioventricular valves are the mitral valve, and the tricuspid valve, which are situated between the atria and the ventricles, and prevent backflow from the ventricles into the atria during systole. they are anchored to the walls of the ventricles by chordae tendineae, which prevent them from inverting. the chordae tendineae are attached to papillary muscles that cause tension to better hold the valve. together, the papillary muscles and the chordae tendineae are known as the subvalvular apparatus. the function of the subvalvular apparatus is to keep the valves from prolapsing into the atria when they close. the subvalvular apparatus has no effect on the opening and closure of the valves, however, which is caused entirely by the pressure gradient across the valve. the peculiar insertion of chords on the leaflet free margin, however, provides systolic stress sharing between chords according to their different thickness. the closure of the av valves is heard as lub, the first heart sound (s1). the closure of the sl valves is heard as dub, the second heart sound (s2). the mitral valve is also called the bicuspid valve because it contains two leaflets or cusps. the mitral valve gets its name from the resemblance to a bishop's mitre (a type of hat). it is on the left side of the heart and allows the blood to flow from the left atrium into the left ventricle. during diastole, a normally-functioning mitral valve opens as a result of increased pressure from the left atrium as it fills with blood (preloading). as atrial pressure increases above that of the left ventricle, the mitral valve opens. opening facilitates the passive flow of blood into the left ventricle. diastole ends with atrial contraction, which ejects the final 30% of blood that is transferred from the left atrium to the left ventricle. this amount of blood is known as the end diastolic volume (edv), and the mitral valve closes at the end of atrial contraction to prevent a reversal of blood flow. the tricuspid valve has three leaflets or cusps and is on the right side of the heart. it is between the right atrium and the right ventricle, and stops the backflow of blood between the two. semilunar valves main articles: aortic valve and pulmonary valve the aortic and pulmonary valves are located at the base of the aorta and the pulmonary trunk respectively. these are also called the "semilunar valves". these two arteries receive blood from the ventricles and their semilunar valves permit blood to be forced into the arteries, and prevent backflow from the arteries into the ventricles. these valves do not have chordae tendineae, and are more similar to the valves in veins than they are to the atrioventricular valves. the closure of the semilunar valves causes the second heart sound. the aortic valve, which has three cusps, lies between the left ventricle and the aorta. during ventricular systole, pressure rises in the left ventricle and when it is greater than the pressure in the aorta, the aortic valve opens, allowing blood to exit the left ventricle into the aorta. when ventricular systole ends, pressure in the left ventricle rapidly drops and the pressure in the aorta forces the aortic valve to close. the closure of the aortic valve contributes the a2 component of the second heart sound. the pulmonary valve (sometimes referred to as the pulmonic valve) lies between the right ventricle and the pulmonary artery, and has three cusps. similar to the aortic valve, the pulmonary valve opens in ventricular systole, when the pressure in the right ventricle rises above the pressure in the pulmonary artery. at the end of ventricular systole, when the pressure in the right ventricle falls rapidly, the pressure in the pulmonary artery will close the pulmonary valve. the closure of the pulmonary valve contributes the p2 component of the second heart sound. the right heart is a low-pressure system, so the p2 component of the second heart sound is usually softer than the a2 component of the second heart sound. however, it is physiologically normal in some young people to hear both components separated during inhalation. development