Heart valves

The heart contains four valves - two atrioventricular (AV) valves (tricuspid and mitral) and two semilunar valves (aortic and pulmonic). Each valve consists of cusps, or leaflets, that open and close in response to pressure changes within the chambers they connect. The primary function of the valves is to keep blood flowing forward through the heart. When the valves close, they prevent backflow, or regurgitation, of blood from one chamber to another. Closure of the valves is associated with heart sounds. Heart valves The two AV valves are located between the atria and ventricles. The tricuspid valve, named for its three cusps, separates the right atrium from the right ventricle. The mitral valve, sometimes referred to as the bicuspid valve because of its two cusps, separates the left atrium from the left ventricle. Closure of the AV valves is associated with S1, or the first heart sound. The cusps of these valves are anchored to the papillary muscles of the ventricles by small tendinous cords called chordae tendineae. During ventricular contraction, the papillary muscles and chordae tendineae work together to prevent the cusps from bulging backward into the atria. Disruption of either structure may prevent complete valve closure, allowing blood to flow backward into the atria. This backward blood flow may cause a heart murmur. Heart valves The semilunar valves are so called because their three cusps resemble half moons. The pulmonic valve, located where the pulmonary artery meets the right ventricle, permits blood to flow from the right ventricle to the pulmonary artery and prevents backflow into the right ventricle. The aortic valve, located where the left ventricle meets the aorta, allows blood to flow from the left ventricle to the aorta and prevents blood backflow into the left ventricle. Increased pressure within the ventricles during ventricular systole causes the pulmonic and aortic valves to open, allowing ejection of blood into the pulmonary and systemic circulation. Loss of pressure as the ventricular chambers empty causes the valves to close. Closure of the semilunar valves is associated with S2, or the second heart sound.