Throughout the period 1977 to 1982, 436 patients underwent aortic valve replacement (AVR), 106 underwent mitral valve replacement (MVR) and 56 patients underwent double valve replacement (DVR), with the Medtronic-Hall prosthetic valve (previous equivalent: Hall-Kaster valve). Early and late mortality were 4% and 9% for AVR, 8% and 11 % for the MVR and 7% and 13% in the DVR, respectively. Actuarial survival after 5 years of follow-up was 80.9% for AVR, 75.4% for MVR and 81.0% for the DVR. Thromboembolic complications included 2 cases of valve thrombosis in the AVR, in one case secondary to valve endocarditis. Eleven further thromboembolic episodes occurred in 10 patients with AVR. In MVR an aspergillus thrombus was found on the valve at autopsy in a patient dying from multiple cerebral aspergillus abscesses. Five further thromboembolic episodes occurred in 4 patients with MVR. In the DVR group there was one valve thrombosis and one further patient with a thromboembolic episode. The actuarial probability of remaining free from thromboembolism at the end of the 5 years of follow-up was 92.5% for AVR and 83.7% for MVR.