Anterior papillary muscle rupture caused by occlusion of the first diagonal branch is reported to be very rare. A 66-year-old woman was transferred to our hospital for acute myocardial infarction and cardiogenic shock. Echocardiography and angiography revealed severe mitral regurgitation caused by rupture of the anterior papillary muscle and the complete occlusion of the first diagonal branch. In an emergent setting, she had been successfully treated by mitral valve replacement and coronary artery bypass grafting. She was discharged on postoperative twelfth day without any event.