Hemodynamic performance of a polyurethane heart valve prosthesis was evaluated in comparison with that of Björk-Shiley Monostrut mechanical valve in steady and pulsatile flow. Pressure losses through the valves were obtained from the streamwise pressure distributions downstream of the valves under steady flow condition. Unsteady and turbulent flow through the heart valve prostheses were investigated using PIV in conjunction with the opening behaviors of valve leaflets. Direct measurements of the wall shear stress by hot-film anemometry (HFA) were compared with the PIV data. By examining the velocity field downstream of the polyurethane heart valve, it is known that high shear stress regions exist at the interface between strong axial jet flows along the wall and vortical flows in the central area. In addition, there are large recirculation regions near the valve, where thrombus formation can be induced by accumulation of damaged blood cells. A correlation between the flow pattern downstream of the valve and the corresponding opening posture of the polyurethane valve leaflet gives useful data necessary for improved design of the superstructure and leaflet geometry of the valve.