An 84-year-old woman was brought to our hospital with cardiogenic shock. Ischemic changes of the ST segment were observed on the electrocardiogram in broad leads, but Q waves were not. Echocardiography revealed severe mitral regurgitation due to prolapse of the posterior leaflet, and coronary angiography showed 2-vessel disease involving left coronary arteries accompanied by a hypoplastic right coronary artery, so the coronary lesion seemed to be equivalent to 3-vessel disease. Preoperative tracheal intubation and intraaortic balloon pump (IABP) were required to maintain the hemodynamics. Emergency surgical procedures of combined coronary artery bypass grafting with mitral valve replacement were performed successfully. After 18 days, the patient was discharged, classified as NYHA class II. The prognosis for acute ischemic mitral regurgitation presenting shock in an octogenarian is extremely poor. Although the clinical symptoms were serious in this case, partial rupture of the papillary muscle and subendocardial infarction contributed to the favorable surgical result.