The four Major Complications- sudden death, infective endocarditis, spontaneous rupture of chordae tendineae, and progressive mitral regurgitation- are examined. Associated Cardiac Diseases, i.e., Marfan's syndrome, ostium secundum atrial septal defect and atherosclerotic coronary artery disease, are discussed, and a section on Treatment deals chiefly with prophylaxis for infective endocarditis and the management of arrhythmias and chest pain.