Medium-term results of valve replacement with a pericardial bioprosthesis were analysed in 141 patients receiving an Ionescu-Shiley aortic prosthesis and in 67 patients receiving a Mitroflow aortic (42), mitral (21) or double mitro-aortic (4) bioprostheses. There were 8 deaths in the operative (5.7%) and medium term (56 months) follow-up periods in the Ionescu group and a cumulative survival of 625 patient-years. There were 16 late deaths, 8 of cardiac origin. The 8 year survival and good functional results rates were 71% and 53% respectively. The linear rates of thrombo-embolism, endocarditis, reoperation, valvular dysfunction and regurgitation were 3.5, 1.1, 2.6, 2.7 and 6.1% patient-years. The corresponding figures in the Mitroflow bioprostheses were 0.5, 1.0, 3.1, 3.1 and 5.6% patient-years, but the average follow-up was shorter (36 months) with a cumulative survival of 195 patient-years. These results underline the frequency of primary valve dysfunction the mechanisms of which are: early tear in areas of high mechanical stress and late calcification. However, the hemodynamic profiles of this type of prosthesis are better than those of porcine bioprostheses which make them a valuable alternative in elderly patients operated for calcific aortic stenosis with a small aortic ring.