Mitral valve insufficiency, also known as mitral regurgitation, is a disease caused by the backflow of blood from the left ventricle to the left atrium due to the incomplete closure of the mitral valve leaflets. Common causes include degenerative valve disease and diseases affecting the heart muscle. Symptoms include dyspnea, fatigue, palpitations, and a holosystolic apical murmur. Complications can include heart failure, pulmonary hypertension, arrhythmias, and pulmonary edema.