Two cases who underwent emergency operation for papillary muscle rupture complicating acute myocardial infarction were presented. The first case was a 75-year-old female who had suffered myocardial infarction 26 days previously. Operation was performed on the 2nd day after onset of mitral insufficiency. The posterior papillary muscle was partially ruptured and the mitral valve was replaced with a mechanical prosthesis (SJM 25mm). The second case was a 76-year-old female who had suffered myocardial infarction 10 days previously. Emergency operation was performed on the 4th day after onset of mitral insufficiency. The posterior papillary muscle was completely ruptured. Mitral valve replacement with a mechanical prosthesis (Omnicarbon 25mm) was performed. In both cases, recovery from cardiogenic shock was not possible preoperatively even with pharmacologic and circulatory support, but the postoperative courses were uneventful in both cases. We recommend immediate surgical intervention for mitral insufficiency in patients with severe grade regurgitation and cardiogenic shock following acute myocardial infarction.