In vivo studies have begun to evaluate a new intraventricular electric axial flow left ventricular assist device (LVAD), the Jarvik 2000, which is a small, valveless pump that is placed inside the left ventricle through the left ventricular apex. The operation, which is performed through a left thoracotomy, may be done without cardiopulmonary bypass and aortic cross-clamping. Outflow is provided through a 16 mm softly woven, Dacron graft anastomosed to the descending thoracic or abdominal aorta. Pump flow, which varies from 2 to 16 l/min in vitro, is changed by adjusting the speed of pump rotation. Preliminary studies were done to evaluate the ease of implantation, hematologic and anatomic compatibility, and pump performance. The device has been implanted in seven healthy, preconditioned calves (83-138 kg), one of which is currently undergoing support. The implantation procedure averaged 3 hours. There were no operative deaths, and blood transfusions were not required. Postoperatively, anticoagulation was achieved with heparin followed by warfarin sodium to maintain prothrombin time or partial thromboplastin time at 1.5-2.0 times baseline. In the six completed studies, support time ranged from 2 to 120 days (mean, 36 days). The seventh calf has been supported for 30 days. In the four long-term studies (20, 70, 120, > 30 days), the mean plasma free hemoglobin values during support were 11.0, 7.7, 6.6, and 3.4 mg/dl, respectively. Under normal conditions, the average daily flow rate ranged from 5 to 6 l/min. During treadmill exercise (10% grade, 1.5 km/h) lasting 20 minutes, peak flow rates exceeded 8 l/min. These pilot studies suggest that this intraventricular axial flow pump is relatively easy to implant, operate, and control. In addition, it is hemocompatible, provides physiologic flow rates, and may be able to provide long-term circulatory support.