The heart is a beating muscle that pumps blood throughout the body. Inside the heart, four valves direct blood flow in the appropriate path. However, a valve that has become narrowed or thickened can compromise blood flow. This condition is called valvular stenosis.

In a healthy heart, two valves control the flow of blood from the upper chambers, or atria, to the lower chambers, or ventricles. Two other valves control blood flow from the ventricles to the lungs and body.

During a normal heartbeat, oxygen-rich blood moves from the left atria to the left ventricle through the mitral valve. The ventricle pumps the blood through the aortic valve to be distributed throughout the body. Oxygen-poor blood moves from the right atria to the right ventricle through the tricuspid valve, and is pumped through the pulmonic valve on its way to the lungs to pick up oxygen.

Thin, fibrous strands called chordae tendineae open and close the flaps, or cusps, of the mitral and tricuspid valves. The chordae tendineae are anchored within the ventricles. When the ventricles contract, the mitral and tricuspid valves are pulled shut while the aortic and pulmonic valves open. The pulmonic and aortic valves open and shut in response to changes in pressure of the atria and ventricles.

If a valve becomes narrow, stiff, or thickened, the heart must work harder to force blood through the smaller opening. Over time, overuse may cause the heart itself to enlarge and thicken. Eventually, heart failure may develop. Valvular stenosis may be present at birth, or it may develop over time as a result of heart or coronary disease.