Clinical results achieved in 100 cases of aortic valve replacement with the Omniscience (O-S) valve during the period from 1980 to 1985 as well as 100 cases of aortic valve replacement with the Omnicarbon (O-C) valve during the period from 1985 to 1989 were studied. Concomitant surgical procedures including mitral valve replacement were performed in 63 patients in the O-S group and 67 patients in the O-C group. Cumulative follow-up in the two groups was carried out for a total of 559 and 273 patient-years, respectively. The overall 4-year actuarial survival rate was 82% +/- 3.8% in the O-S group and 89.5% +/- 3.2% in the O-C group, the corresponding rates for patients undergoing isolated aortic valve replacement being 82.9% +/- 4.2% in the O-S group and 91.9% +/- 3.5% in the O-C group. The overall 4-year actuarial event-free rate with respect to thromboembolic complications was 88.8% +/- 3.3% in the O-S group and 94.4% +/- 2.8% in the O-C group, as compared with the corresponding rates of 89.2% +/- 3.6% in the O-S group and 95.9% +/- 2.8% in the O-C group for patients undergoing isolated aortic valve replacement. The overall rate of valve-related complications, including thromboembolism, anticoagulant-related hemorrhage, perivalvular leak, infection, and structural failure, was 78.8% +/- 4.2% in the O-S group and 89.3% +/- 3.5% in the O-C group (p less than 0.05), and for isolated aortic valve replacement, 79.7% +/- 4.5% in the O-S group and 89.6% +/- 4.1% in the O-C group.(ABSTRACT TRUNCATED AT 250 WORDS)