Acquired heart valve defect in which the mitral valve (between the left atrium and left ventricle) no longer closes properly. Through this leak, the blood partially flows back into the left atrium during systole and leads to an enlargement of the left atrium and left ventricle due to the blood volume load. The left ventricle can thus only pump part of the blood volume on into the aorta, the consequence being the reduced pumping capacity of the left ventricle. Causes can be inflammation or tearing of tendon sutures or of retaining muscles of the tendon sutures of the mitral valve, which anchor the leaflets in the wall of the left ventricle.