The CarboMedics and Monostrut mechanical valve prostheses were compared in the aortic position. Among 200 consecutive patients, 100 received the CarboMedics (CM) prosthesis and 100 the Monostrut (M). Patients in both groups were similar in terms of preoperative and surgical characteristics. Mean follow up was 5.58 years (total 1,097 pt-yr). Early mortality rates for the CM and M groups were 1% and 3%, respectively; late mortality rates were 7% and 9%. Survival at 11 years was 80.51 ± 7.36% for CM, and 79.62 ± 5.59% for M prostheses. Rates of thromboembolism were 1.03% and 0.20% per pt-yr for the CM and M groups, respectively; rates of hemorrhage were 0.71% and 0.61% per pt-yr; rates of paravalvular leak were 0.35% and 0% per pt-yr; and postoperative NYHA classes I-II were 95.83% and 94.37%. The results with both prostheses were excellent, and neither demonstrated any superiority over the other.