Development of an implantable electric motor ventricular assist device was initiated at The Pennsylvania State University in 1978. The first system developed utilized a drum cam and cam followers to convert rotary to rectilinear motion. This initial system weighed over one kilogram. The system was subsequently redesigned to utilize a roller screw mechanism (Transrol or Rollvis). The use of the roller screw mechanism reduced the weight of the energy converter to below 700 grams. To date, 33 calves have had long-term left ventricular to aortic assistance with a hermetically sealed roller screw device, with continuous pumping for as long as 235 days. Two of these animals have had completely implanted systems with telemetry. The system currently in use consists of a totally implanted blood pump, energy converter, electronics and implanted battery, along with a transcutaneous energy transmission system. This system employs no percutaneous leads; all energy is transmitted transcutaneously by inductive coupling. This is the only system currently undergoing in vivo evaluation that utilizes transcutaneous energy transmission and two-way telemetry. Continued in vivo and in vitro testing will be conducted in an effort to refine the design.