The three components of the Novacor left ventricular assist system, compact controller, battery, and back-up battery, have been miniaturized in the development of the wearable system. Therefore patients can be fully mobilized receiving mechanical circulatory support while awaiting heart transplantation. Between February 1992 and April 1994 a total of eight patients with decompensated heart failure (6 dilated cardiomyopathy, 1 acute myocarditis, 1 ischemic cardiomyopathy) were treated with the Novacor left ventricular assist systems. In the most recent four cases the wearable system (N100P) was used. Patients' ages ranged from 17 to 49 years. In five patients severe failure of the right side of the heart was present at the time of implantation. Hemodynamic stabilization was achieved in all patients during the 2 to 122 days (mean 30.8 +/- 42.5 days) of support. The following parameters were measured on average before and 24 hours after implantation of the left ventricular assist system: mean arterial pressure 70 +/- 11 versus 87 +/- 13 mm Hg (p < 0.05), cardiac index 1.71 +/- 0.42 versus 3.23 +/- 0.74 L/min/m2 (p < 0.05), pulmonary capillary wedge pressure 27.1 +/- 4.4 versus 9.9 +/- 5.2 mm Hg (p < 0.01), mean pulmonary pressure 41 +/- 9 versus 27 +/- 6 mm Hg (p < 0.05), and right ventricular ejection fraction 16.7% +/- 10.3% versus 22.0% +/- 11.6% (not significant). Patients who received the wearable system were capable of managing their own power supply during the bridging period and were able to walk to the hospital park and shopping area. One patient had a serious pulmonary infection, which was treated successfully, and two patients had a cerebrovascular accident, which resolved in one and resulted in a minor residual deficit in the other. All eight patients received a heart transplant. One patient died early after transplantation and seven patients are alive and well. In summary, the wearable Novacor left ventricular assist system provides major advantages regarding quality of life of patients during mechanical circulatory support. However, there is a remaining risk of thromboembolism despite anticoagulation therapy.