Design limitations of current mechanical heart valves cause blood flow to separate at the leaflet edges and annular valve base, forming downstream vortex mixing and high turbulent shear stresses. The closing behavior of a bileaflet valve is associated with reverse flow and may lead to cavitation phenomenon. The new trileaflet (TRI) design opens similar to a physiologic valve with central flow and closes primarily due to the vortices in the aortic sinus. In this study, we measured the St. Jude Medical 27 mm and the TRI 27 mm valves in the aortic position of a pulsatile circulatory mock loop under physiologic conditions with digital particle image velocimetry (DPIV). Our results showed the major principal Reynolds shear stresses were <100 N/m2 for both valves, and turbulent viscous shear stresses were smaller than 15 N/m2. The TRI valve closed more slowly than the St. Jude Medical valve. As the magnitudes of the shear stresses were similar, the closing velocity of the valves should be considered as an important factor and might reduce the risks of thrombosis and thromboembolism.