Forty three year-old male who had cough and easy fatigability since three weeks prior to admission was diagnosed to have acute pulmonary edema with severe mitral regurgitation caused by active infective endocarditis. Transesophageal echocardiograms under the endotracheal intubation for controlled respiration suggested rupture of the posterior papillary muscle of the mitral valve and the emergency surgical treatment was performed. Intraoperatively the total rupture of the posterior papillary muscle was confirmed and mitral valve replacement was carried out with a SJM prosthetic valve. Histological examination of the ruptured papillary muscle revealed hemorrhage, muscle necrosis and small cell infiltration suggesting the presence of active inflammation with bacteria on it. Staphylococcus epidermidis was demonstrated by the bacteriological studies of the ruptured papillary muscle.