A total of 158 patients who received Biocor porcine bioprostheses, and 100 who received St. Jude Medical (SJM) mechanical valves were investigated retrospectively ten years after valve implantation. Preoperatively, mean age and male:female sex ratio were similar in both groups. Early mortality was 4% in both groups, the major cause being congestive heart failure. Ten-year survival was similar in each group (77.8 ± 3.3% versus 81.0 ± 3.9%; p = 0.538). Ten-year freedom from reoperation was lower in the Biocor group than in the SJM group, though not statistically significantly so (84.9 ± 3.2% versus 92.2 ± 2.8%; p = 0.206). Biological prostheses should be used selectively in elderly patients whose expected survival is <10 years, in patients in sinus rhythm, and in young females wishing to have children.