The most widely implanted prosthetic valve is the mechanical bileaflet. Recent clinical experiences suggest that some designs are more prone to thromboembolic episodes than others. This study evaluated the hinge flow and near-field forward flow of the new St. Jude Medical Regent bileaflet mechanical heart valve. Laser Doppler velocimetry measurements were conducted within the hinge and near-field forward flow regions of the Regent valve. These pulsatile flow velocity measurements were animated in time to visualize the flow fields throughout the cardiac cycle. During forward flow, a recirculation region developed in the inflow pocket of the Regent hinge but was subsequently abolished by strong backflow during valve closure. Leakage velocities in the hinge region reached 0.72 m/s and Reynolds shear stresses reached 2,600 dyn/cm2. Velocities in the near-field region were highest in the lateral orifice jet, reaching 2.1 m/s. Small regions of separated flow were observed adjacent to the hinge region. Leaflet motion through the Regent hinge creates a washout pattern which restricts the persistence of stagnation zones in its hinge. Based upon the results of these studies, the hematological performance of the Regent series should be at least equivalent to the performance of the Standard series.