Surgical patients who cannot be weaned from cardiopulmonary bypass during operation or who develop balloon-dependent left ventricular failure postoperatively are now considered unsavable. However, in those with potentially reversible ventricular dysfunction, recovery might be possible if an improved means of temporary circulatory support were available. Towards this end, a pneumatically actuated, left ventricular assist pump was developed and evaluated in 20 consecutive calf experiments. The device, containing a flexible polyurethane pumping chamber, was positioned on the chest wall and connected to the left ventricular apex and descending thoracic aorta by two Dacron valved conduits (xenograft valves). All animals survived a 14 to 30 day pumping interval, and 7 underwent successful removal of the device by division of the Dacron conduits below skin level. As a prelude to human investigation, pumps were implanted during a series of routine autopsies through midline sternotomy incison. The device was positioned on the right anterolateral chest wall, with two valved conduits traversing the mediastinum to connect the pump to the left ventricular apex and ascending aorta.