A 70-year-old man with a Duromedics mitral valve prosthesis had two episodes of infective endocarditis caused by enterococcus (1994 and 1996). Colonoscopy revealed five polyps. Surgical resection was performed and 2 days later the patient had dyspnea and fever. Because of a suspected valve thrombosis, intravenous heparin was given which resulted in hematic effusion in the Douglas' cul-de-sac. Intravenous heparin was withdrawn but the patient continued to have a worsening dyspnea, hyperthermia and hypotension. The patient was transferred to our Institution in cardiogenic shock. Acute thrombosis of the valve was diagnosed by echocardiography, and the patient died before transesophageal Doppler echocardiography was performed. Post mortem examination revealed mitral valve infective thrombosis. In patients with valvular prostheses, endocarditis is an added thromboembolic risk.