Fifty-seven patients underwent aortic valve replacement with a stentless glutaraldehyde-fixed bioprosthesis; 27 received a porcine aortic valve and 30 had a bovine pericardial valve. Two groups of 30 patients each who had aortic valve replacement with a tilting-disc mechanical valve or a stented porcine bioprosthesis served as controls. There were no differences in sex, body surface area, valve lesion, and valve size among the four groups. Results were assessed on a Doppler-based determination of maximum velocity across the valve, aortic valve area, and degree of valve regurgitation. Velocity across the valve was significantly less with stentless pericardial valves than with stentless porcine valves, stented bioprostheses, and mechanical valves. Stentless valves had a significantly larger aortic valve area when compared with stented valves. Mild central aortic insufficiency was detected more often with stentless pericardial than with stentless porcine bioprostheses (p = 0.04). Stentless valves showed a higher incidence of complete atrioventricular block when compared with stented valves (p = 0.04). Long-term studies are now warranted to assess the durability of both types of stentless valves.