Disc immobilization caused by an unraveled suture in a mitral valve prosthesis represents a rare extrinsic complication in heart valve replacement. We report a case of a 54-year-old white male who underwent mitral valve replacement because of a severe mitral regurgitation. A Björk-Shiley tilting disc was implanted with interrupted "U" shaped 3/0 silk sutures. There were no complications and the patient was discharged in the 10th postoperative day. Twenty days after surgery the patient died for acute pulmonary edema. Autopsy revealed an unraveled suture producing interference with the tilting disc as a cause of disc prosthesis immobilization in closed position. The possible explication of this rare complication is the combination between unraveled suture and the pleating held by Teflon sewing ring after restoring heart function. A flaccid heart can produce an overestimation of the annulus size and the valve ring can bring an anomalous interference with the valve mechanism. In conclusion disc immobilization by an unraveled suture is a complication that can occur very rarely but an accurate prevention must be warrant particularly with a tilting disc more than a beleaflet prosthesis.