Thermal management of the implantable ventricular assist system (VAS) is important not only from the pathophysiological point of view but also from the standpoint of system endurance. The heat distribution within the Baylor VAS was measured using different motor housing materials and environmental conditions. The temperature of the circulating water in the mock loop was set at 37 degrees and 42 degrees C. A polycarbonate motor housing was not a suitable material because of the high temperature development in the actuation system. An anodized aluminum housing demonstrated excellent heat conductivity. The surface temperature of this motor housing was 41.6 degrees C when immersed in circulating water at 42 degrees C. Heat conduction from the motor to the circulating blood revealed an effective thermal path. In the worst case, the heat flux of the motor to the circulating blood revealed an effective thermal path. In the worst case, the heat flux of the motor housing was calculated to be less than 0.062 W/cm2--an acceptable level for the surrounding tissues.