Acute mitral regurgitation is a disorder in which the heart's mitral valve suddenly does not close properly, causing blood to leak (back-flow) into the left atrium (upper heart chamber) when the left ventricle (lower heart chamber) contracts.

Regurgitation (leaking from insufficient valve closure) is caused by diseases that weaken or damage the valve or its supporting structures. Inadequate closure of the mitral valve causes blood to flow back to the left atrium. The blood flow to the rest of the body is decreased as a result and the heart may pump harder to try to compensate.

Acute mitral regurgitation may be the result of dysfunction or injury to the valve following a heart attack or infective endocarditis (infection of the heart valve). These conditions may rupture the valve, the papillary muscle or chordae tendineae (the structures that anchor the valve cusps). A rupture of these structures results in the valve leaflet prolapsing or flailing (protruding) into the atrium, leaving an opening for the backflow of blood.

Risk factors include a recent individual history of the disorders mentioned above.

See also: Chronic mitral regurgitation.

• Rapid breathing
• Shortness of breath that increases when lying flat (orthopnea)
• Sensation of feeling the heart beat (palpitations)
• Chest pain -- unrelated to coronary artery disease or a heart attack
• Cough

Palpation may show thrill (vibration) over the heart. A stethoscope may reveal a distinctive murmur in the heart. However, this murmur may be absent in some cases of acute mitral regurgitation. If fluid backs up into the lungs, there may be crackles heard in the lungs. An extra heart sound (S4 gallop) may also be heard.

Blood pressure is usually normal.

The following tests may be performed:

• Echocardiogram 
• Color flow Doppler exam
• Transesophageal echocardiogram (TEE)
• Cardiac catheterization 
• Chest x-ray - may also show fluid in the lungs or prominent pulmonary veins.
• Swan-Ganz (right heart catheterization)  - may show high left atrial pressure. 
• ECG - usually shows a normal sinus rhythm but may show arrhythmias 
• Chest MRI scan 
• Radionuclide scans
• CT scan of the chest