Fluid-pumping technology is a mature engineering subject area with a well-documented knowledge base. However, the pump design optimization techniques accepted in industry are geared toward steady-state constant-flow conditions. In contrast, the implantation of a continuous-flow pump to aid the output of the human left ventricle subjects the device to perpetual variation. This study measures pressure-flow performance characteristics for both axial- and centrifugal continuous-flow rotary blood pumps across a wide range of pressure differential values under uniform conditions by means of a novel open-loop flow system. The axial-flow devices show lower hydraulic efficiency. All pumps yield best efficiency point at a head to flow coefficient ratio of approximately 1.7. The open-loop flow system accounts for the dynamic changes associated with human heart physiology and allows for more precise characterization of existing heart pumps and those in development.