Between 1975 and 1979 140 cardiac bioprostheses were implanted in 133 patients (mean age 60 years) at Papworth Hospital, Cambridge, England. Of these 85 remained available for analysis in the mid- and long term. Incidence of thromboembolism, bleeding, and infectious endocarditis were 2.1% +/- 0.6% (Standard error of mean), 0.2% and 0.8% +/- 0.4% per patient-year respectively. Primary valve failure occurred in only 5 patients. Freedom from primary valve failure was 98.3-r +/- 0.3% at 10 years and 82.3 +/- 4.5% at 12 years after replacement. Many patients died of old age before valve failure could occur. Therefore the percentage of tissue failure compared with the original number of patients operated on is even lower. Low incidence of valve failure, lack of need for long-term anticoagulation, and low incidence of thromboembolism make the bioprosthesis a good choice for valve replacement in older patients.