The Heart Mitral Valve

The mitral, or bicuspid, valve lies between the left atrium and ventricle. One of the heart's four valves, it is the only one with two, rather than three, flaps. As viewed from underneath, an opened valve shows that attached to each valve flap there are tough, inelastic tendons, which in turn are anchored to papillary muscles, extensions of the ventricle wall. When blood is pumped into the ventricle from the atrium the papillary muscles relax, allowing the flaps to move apart and the valve to open. When the ventricle contracts, to force blood into the aorta, the attached papillary muscles also contract. This puts tension on the tendons, which pull the flaps together to prevent a backflow of blood.