We report the history and course of a patient in whom a left ventricular-coronary sinus fistula developed following mitral valve replacement due to prosthetic endocarditis. Six months after the intervention the patient suddenly presented with deterioration of her symptoms, holosystolic murmur and signs of congestive heart failure. Transesophageal echocardiography showed a left-to-right shunt but did not show its exact location. At surgery, exploration of the right atrium revealed a left ventricular-coronary sinus communication due to discontinuation of the left ventricular free wall next to the coronary sinus; repair of the defect was successfully performed by direct suture. The postoperative course was uneventful and the patient recovered quickly. This case is reported to stress that debridement of the mitral annulus and removal of an old prosthesis must be very carefully performed and to facilitate the diagnosis of this rare but severe complication of repeated mitral valve replacement.