Heart valve

A heart valve is a specialized structure set in an opening of the heart, and it has a single job: to keep blood moving in one direction so that it does not flow back. It is a door that opens only one way.

There are two groups, told apart by where they sit. The ones placed between an atrium and a ventricle, that is, between the chamber that receives and the one that pumps out, are called atrioventricular. The ones at the outlets toward the pulmonary trunk and toward the aorta, the two great arteries that leave the heart, are called semilunar.

What keeps the atrioventricular valves from flipping backward is an anchoring system. Each leaflet, which is one panel of the door, is attached to strong cords of connective tissue called chordae tendineae, and those cords are tied to a papillary muscle that rises from the floor of the ventricle. When the ventricle contracts forcefully, the tension in those cords holds the leaflet in place and keeps blood from flowing back into the atrium. The cords are the hinges that keep the door from swinging backward.