Any of four structures (two semilunar valves [pulmonary valve, aortic valve], the mitral valve, and the tricuspid valve) within the heart that, by closing and opening, control blood flow in the heart and permit flow in only one direction.
The structure at the exit of each of the four chambers of the heart that allows blood to flow out, but prevents backflow. The mitral valve separates the left atrium of the heart from the left ventricle. The tricuspid valve divides the right atrium from the right ventricle. The pulmonary valve controls blood flow from the right ventricle into the pulmonary artery, which leads into the lungs. The aortic valve performs the same function between the left ventricle and the aorta, the artery that leads to the rest of the body.