A single aortic valve replacement using the lonescu-Shiley bovine pericardial xenograft valve was performed in 66 consecutive patients during the period from February, 1979 to June, 1984. They were 49 males and 17 females with ages ranging from 9 to 61 [mean, 31.113.1] years, and 9 of them were children younger than 15 years of age. Twenty-seven patients [40.9%] required the combined operative procedures to either other valvular lesions or congenital defects. There were 9 early deaths within 30 days of surgery [operative mortality rate, 13.6%] and 2 late deaths thereafter [late mortality rate, 3.0%; or 1.75%/patient-year]. The 57 early survivors were followed for a total duration of 114.2 patient-years [mean, 24.016.0 months]. Four patients experienced thromboembolic complication with no death [3.50%/patient-year]; one died from intracranial bleeding related to anticoagulation [0.88%/patient-year]; one recovered from prosthetic valve endocarditis [0.88%/patient-year]; and four developed aortic regurgitant murmur with none or minimal cardiac symptoms and they were classified into cases of tissue valve failure [3.50%/patient-year]. The actuarial survival rate was 82.34.7% at 6 years, and the actuarial probabilities of freedom from thromboembolism and valve failure were 93.33.9% and 89.15.8% at postoperative 6 years respectively Symptomatic improvement was excellent in most late survivors at the follow-up end with the mean of NYHA Classes of 1.040.19 while the one was 2.290.67 at the time of operation. Excluding the higher operative mortality rates, these clinical results are fully comparable with the ones of reports from the major institutions using the porcine aortic or the bovine pericardial tissue valves and warrants the continued use of the xenograft valve in the aortic position. The importance of more detailed preoperative evaluation of the myocardial function and the need of improved myocardial preservation during surgery for the improved early clinical results were discussed.