The purpose of this study was to evaluate unloading effects and establish optimal control methods of a novel intraventricular cardiac assist device, the Jarvik 2000 (J2K). In three calves, the J2K was implanted using cardipulmonary bypass. After stabilization, left ventricular (LV) performance and coronary blood flow (CBF) rate were evaluated at different pump speeds. With increasing pump speed, the pump flow (PF) rate steadily rose up to 5.1 ±0.4 L/min at 12,000 rpm (see table 1). Mean blood pressure (MBP) was maintained well, while LV volume diminished constantly. Left ventricular pressure (LVP) did not change remarkably from baseline through 8000–10,000 rpm, but declined at 11,000 rpm and further decreased at 12,000 rpm. Similarly, both CBF and myocardial oxygen consumption (MVO2) were kept relatively constant at a range of 8000–10,000 rpm, but decreased at 11,000 rpm. They significantly dropped at 12,000 rpm, concomitantly with cessation of the aortic valve opening. In conclusion, the decrease in MVO2 indicated that J2K could effectively unload the left ventricle at higher pump speeds, reducing cardiac work by more than 30%. However, excessive unloading may lead to extreme CBF reduction and enhance a potential risk of clot formation in diseased coronary arteries. It may be an advantageous strategy for optimal device control to adjust the pump speed periodically, avoiding persistent closure of the aortic valve.Table