Chronic mitral valve regurgitation
Chronic mitral valve regurgitation is caused by diseases or conditions that damage the mitral valve over time. The valve then allows blood to leak backward (regurgitate).

The mitral valve may become hard, or calcified, around the tough ring of tissue (annulus) to which the mitral valve flaps are attached. Normally the mitral annulus is soft and flexible. But as a person ages, calcium may build up inside the annulus. This hardened mitral valve cannot close completely, and blood leaks backward (regurgitates) into the upper left chamber of the heart camera.gif (atrium).

Examples of diseases or conditions that can cause mitral valve regurgitation include:

Mitral valve prolapse.
Heart defects or abnormalities present at birth (congenital heart defects).
Endocarditis, which is an infection of the lining of the heart and heart valves. This infection can scar the mitral valve.
Injury to the heart or the chordae tendineae, which are strong, flexible cords that control the opening and closing of the mitral valve.
Dilation of the left ventricle, or heart failure. This can be caused by years of high blood pressure, coronary artery disease, or heart muscle disease (cardiomyopathy).
Autoimmune diseases that can damage the mitral valves, such as rheumatoid arthritis or lupus.
Marfan's syndrome, which is a connective tissue disease.
Severe kidney disease.
Rheumatic fever, which can scar the heart valves and prevent them from closing completely.
Previous use of the weight-loss medicine fen-phen (phentermine and fenfluramine/dexfenfluramine), which appears to increase the risk of heart valve disease.
Acute mitral valve regurgitation
Acute mitral valve regurgitation occurs when the mitral valve or one of its supporting structures ruptures suddenly, creating an immediate overload of blood volume and pressure in the left side of the heart. Your heart doesn't have time to adjust to the increased volume and pressure of blood (as it does in chronic MR).

Causes of sudden rupture include:

Injury to the chordae tendineae. Endocarditis may also cause the chordae tendineae to rupture.
Injury to the chest.
Heart attack, which may cause the rupture of the muscle (papillary) surrounding the valve.
Problems with a prosthetic mitral valve.
Perforation of the mitral valve flap (leaflet), caused by endocarditis.