Heart Valves

The heart contains four valves that act as one-way doors, ensuring blood flows in a single direction through the chambers and out to the great vessels. They open and close passively in response to pressure changes during each cardiac cycle, and their closing produces the familiar "lub-dub" heart sounds.

Atrioventricular Valves

Two atrioventricular (AV) valves sit between the atria and ventricles. The tricuspid valve, with three leaflets, separates the right atrium from the right ventricle. The mitral valve (also called the bicuspid valve), with two leaflets, separates the left atrium from the left ventricle. Each AV valve is supported by an apparatus of fibrous cords called chordae tendineae that anchor the leaflets to papillary muscles in the ventricular wall. When the ventricles contract, these structures hold the leaflets shut and prevent blood from leaking backward into the atria.

Semilunar Valves

The two semilunar valves guard the exits from the ventricles into the great arteries. Each has three cup-shaped (sinus-like) leaflets attached to a fibrous annulus. The pulmonary (pulmonic) valve lies between the right ventricle and the pulmonary artery, and the aortic valve lies between the left ventricle and the aorta. When the ventricles relax, blood in the arteries falls back against these leaflets and snaps them closed, preventing backflow into the heart.

Clinical Relevance

Valve problems generally fall into two categories. Stenosis is narrowing that limits forward flow, forcing the heart to work harder; aortic stenosis is a common example in older adults. Regurgitation (insufficiency) is leakage that allows blood to flow backward, as in mitral regurgitation. Valves can also become infected (endocarditis) or be damaged by congenital conditions or rheumatic fever. Severely diseased valves may be repaired or replaced surgically or via catheter-based procedures. This information is educational and not a substitute for evaluation by a clinician.