The mitral valve is located between the heart’s left atrium (upper chamber) and left ventricle (lower chamber). As oxygenated blood returns to the left atrium from the lung, the atrium eventually fills, forcing the valve open, and blood is pumped through to the left ventricle and to the rest of the body via the aorta. The most common disease to affect the mitral valve is mitral regurgitation (MR). This is when blood leaks backward through the mitral valve when the left ventricle contracts, and means that the heart has to work harder to push blood around the body. 

Symptoms of MR include fatigue, shortness of breath and worsening heart failure. The condition can also place further pressure on the heart’s pulmonary blood vessels (which carry blood between the heart and lungs) and, in severe cases, this can result in congestion in the lungs.