The St Jude Medical prosthesis on the aortic valve was evaluated in a 7-year prospective study which involved 49 patients. Survivors were followed up for 2,577 patient-months, meaning a mean follow-up of 5 years per patient and a minimum follow-up of 4 years per patient. The overall survival rate at 6 years was 79.6 +/- 5.7 p. 100. All deaths occurred during the first two years, and none of them was ascribable to the prosthesis. The left ventricular systolic and diastolic echocardiographic diameters were significantly greater in the patients who died. The linear rate of thromboembolic accidents was 0.93 p. 100 per patient-year, and that of accidents due to anticoagulants was 3.26 p. 100 per patient-year. The probability of freedom from all complication at 6 years was 71 +/- 9 p. 100. In the totality of patients, 10.2 p. 100 required pacemaker implantation; these patients had aortic stenosis exclusively, and all were alive at 7 years. The quality of live, assessed during consultations, was altered in one-half of the survivors. The good results obtained with the St Jude Medical prosthesis are marred by a high initial mortality rate, notably in patients with left ventricular enlargement, by the frequency of accidents due to anticoagulants and by the mediocre quality of life of survivors.