Background-Continuous-flow rotary pumps with axial design are increasingly used for left ventricular assist support. The efficacy of this design compared with pulsatile, volume displacement pumps, with respect to characteristics of left ventricular unloading, and exercise performance remains largely unstudied. Methods and Results-Thirty-four patients undergoing implantation with a pulsatile, volume displacement pump operating in a full-to-empty cycle (HeartMate XVE; Thoratec Inc, Pleasanton, Calif; nĎ16) or continuous-flow rotary pump with an axial design operating at a fixed rotor speed (HeartMate II; Thoratec Inc; nĎ18) were evaluated with right heart catheterization and echocardiography preoperatively and at 3 months postoperatively and cardiopulmonary exercise testing 3 months postoperatively.