The mitral valve is one of four valves in the heart. It regulates blood flow from the upper left chamber (left atrium) into the lower left chamber (left ventricle). The left ventricle is the heart's main pumping chamber.

A normal mitral valve has two flaps, or leaflets. When the heart pumps, blood forces the flaps open, and blood flows from the left atrium to the left ventricle. Between heartbeats, the leaflets close tightly so that blood does not leak backwards through the valve.