A person with mitral regurgitation has a leaky mitral valve.

A normal mitral valve allows blood to flow from the left atrium, into the left ventricle. The mitral valve closes to prevent the backflow of blood from the left ventricle into the left atrium.

Mitral regurgitation results when the mitral valve does not completely close, due to scarring, thickening, or malformation of the valve. Blood leaks from the left ventricle, into the left atrium.