Papillary muscle rupture is one of the common complications of acute myocardial infarction. We report a case of 77-years-old man with an acute posterior papillary muscle rupture without obvious coronary artery disease. The patient presented with cardiogenic shock and pulmonary edema. Emergency coronary angiogram showed no obstruction in coronary arteries. An echocardiogram and right heart catheterization data suggested acute mitral regurgitation caused by ruptured posterior papillary muscle. Percutaneous cardiopulmonary support was induced because of his unstable hemodynamics, and then emergency mitral valve replacement was performed. Intraoperative findings suggested some ischemic changes in the posterior papillary muscle. Pathologically, both old and new ischemic lesion presented in the same papillary muscle. Moreover, severe thickening of a small vessel wall was noted. This case presented one of the possible mechanisms of so-called idiopathic papillary muscle rupture.