heart valve, one of the four structures within the heart that prevent backflow of blood by opening and closing with each heartbeat. The valves include two semilunar valves, the aortic and pulmonary; the mitral or bicuspid valve; and the tricuspid valve. The valves permit blood flow in only one direction; any of the valves may become defective, permitting the backflow associated with heart murmurs. Also called cardiac valve. See also heart, mitral valve, semilunar valve, tricuspid valve.
