Valve replacement with an Angell-Shiley bioprosthesis was accomplished in 449 patients. To evaluate the bioprostheses from this total series, 344 patients who did not undergo associated operation, had no previous operations, or had no other valve substitutes were selected. Hospital mortality was 2.6% for aortic (4 out of 156), 7.2% for mitral (9 out of 125), and 12.7% for multiple-valve replacements (8 out of 63). The 323 patients discharged from the hospital were followed for 6 to 36 months. There were 15 late deaths. Hepatitis, bleeding, thromboembolism, endocarditis, and residual valvular incompetence, always periprosthetic, were the major complications. Forty-five patients with single-valve replacement (16 mitral and 29 aortic) without clinical valve dysfunction were electively recatheterized to assess hemodynamic performance. Measurements were recorded at rest and during exercise on a bicycle ergometer. Functional aortic valve orifice averaged 1.23 +/- 0.33 cm2 and the mean systolic gradient was 21.51 +/- 6.68 mm Hg at rest. During exercise, aortic gradient increased to 26.60 +/- 7.54 mm Hg and mean functional area to 1.51 +/- 0.34 cm2. In the mitral position, the mean diastolic gradient at rest was 8.44 +/- 3.17 mm Hg and the functional orifice area averaged 1.67 +/- 0.51 cm2. Exercise increased the mean gradient to 11.92 +/- 3.8 mm Hg and the mean orifice area to 2.05 +/- 0.57 cm2.