The Hancock (H) and Carpentier-Edwards (CE) porcine xenografts are the most commonly used bioprostheses hemodynamic performance of these valves at each valve size was assessed by intraoperative measurement of transvalvular gradients and cardiac outputs in 122 patients undergoing aortic or mitral valve replacement. At comparable cardiac outputs, peak aortic valve gradients (+/- DS) were: 23-mm valve - H (modified orifice) 10.8 +/- 5.9 mm Hg, CE 7.6 +/- 6.2 mm Hg; 25-mm valve - H 11.9 +/- 5.5 mm Hg, CE 8.3 +/- 5.9 mm Hg; 27/29-mm valve - H 11.0 +/- 6.0 mm Hg, CE 6.6 +/- 5.0 mm Hg. Mitral valve gradients were: 29-mm valve - H 3.7 +/- 1.2 mm Hg, CE 2.8 +/- 1.1 mm Hg; 31-mm valve - H 3.5 +/- 1.0 mm Hg, CE 2.6 +/- 0.7 mm Hg, 33/35-mm valve - H 3.2 +/- 1.9 mm Hg. In both the mitral and aortic positions, Carpentier-Edwards porcine bioprostheses had significantly lower (p less than 0.01 and P less than 0.05, respectively) transvalvular gradients than Hancock porcine xenografts.