A new ventricular assist device (VAD) pneumatic driver with a servomatic left atrial pressure (LAP) control mechanism was developed for easy and safe control of left ventricular assist devices. The negative driving pressure (NP) can be automatically varied to control the assisted circulatory flow (AF), comparing the patient's LAP with prescheduled LAP (s-LAP). Animal experiments revealed this servomatic control system to be useful.