Background: In patients being considered for aortic valve replacement, there remains controversy over which design or tissue offers the best performance.Previous studies have demonstrated superior resting haemodynamics with the stentless design, but these results have not been substantiated by others.We therefore aimed to evaluate in a single study, the haemodynamic performances at rest and stress of 5 different widely-used aortic valve prostheses: stentless porcine xenograft, stentless bovine pericardium, stented porcine xenograft, stented bovine pericardium and mechanical.We also compared them to normal aortic valves, and stenosed valves of variable severity.Methods and Results: Pre-operative echocardiography, and dobutamine stress echocardiography at 1 year postoperatively, were undertaken in 106 patients (n=1 8-24 from each group).Stress echocardiograms were also performed on 97 patients with normal trileaflet aortic valves, or aortic stenosis of varying severity.Regardless of type of prostheses, there were no differences in left ventricular mass reduction at 1 year.However, during both rest and dobutamine stress, the stentless bioprostheses, whether porcine or bovine, displayed superior haemodynamics across nearly all echocardiographic parameters when compared to stented or mechanical prostheses.Comparing both stented designs, the stiffer bovine tissue performed worse at rest, but with stress, the bovine stented valve performed as well as the porcine stented valve.The mechanical prosthesis and stented bioprostheses had higher resistances than the stentless prostheses; the mechanical and stented valves had similar stress haemodynamics.No prosthesis could perform as well as a normal, native trileaflet aortic valve.During stress, the performances of the stentless bioprostheses were similar to the mildly stenosed native aortic valve, whereas performances of the stented and mechanical prostheses were closer to native valves with mild-to-moderate stenoses.Conclusions: Stentless bioprostheses, regardless of tissue type, displayed superior haemodynamics at rest and during pharmacological stress, compared with stented or mechanical prostheses.Stent design was therefore more important than tissue type for performance, with the stentless prostheses giving the closest performance to a normal, native aortic valve.