A total of 61 VASs developed in Tokyo University were evaluated at 21 institutions in the period 1985-1989 for determination of its reliability and effectiveness. The system is comprised of a pneumatic sack-type pump (Nippon Zeon Co.), and its driving console (Aishin Seiki Co.). The stroke volume of the pump is 40 ml and blood contacting surfaces are coated with Cardiothane. Ages of the patients (pts) ranged from 12-82 yrs (mean 58 yrs). VASs were used in the assist mode of LVAD (54 pts), RVAD (5 pts) and BVAD (2 pts). Most of the cases (58 pts) included postocardiotomy cardiogenic shock after surgery for ischemic (28 pts), valvular (22 pts), both ischemic and valvular (7 pts) and congenital (1 pt) heart diseases. Average duration of the assist ranged from 1 hr-20 days (mean 5.6 dys). The VADs could be weaned in 34 cases (56%) and among these, 13 cases (21%) survived to discharge from the hospital. Causes of death in cases which could be weaned from the VAD included multiple organ failure/due to delayed institution of adequate circulatory support, renal failure and systemic infection. Small and minute thrombus formations were noted in 7 cases however, no pump originated thromboembolism were complicated. No troubles of the pump including leakage nor breakage, no mechanical failures of the driving consoles were experienced in any of the cases. Thus, it is concluded that the system was proved to be clinically effective and reliable.