Precise regulation of output voltage (motor voltage) and monitoring of the implanted pump were obtained with a transcutaneous energy transmission system. Information on both motor voltage and pump stroke is transmitted through the skin by frequency-modulated infrared pulses using a light emitting diode and a phototransistor. The motor voltage is compared with the nominal value, and the duty cycle of the primary pulse is regulated according to the error signal. Infrared pulses up to 100 KHz were transmitted through porcine muscle up to 1 cm thick. Both the pump stroke and motor voltage signals were transferred across the muscle without interference. The output voltage was kept almost constant for the change in tissue gap of 3-8 mm and of 0-10 mm in radial displacement. The system developed is useful for implantable artificial hearts.