A nonpulsatile perfusion apparatus, based on the air-lift pump principle, has been developed. Circulation of the perfusate, as well as oxygenation and maintenance of acidbase balance, is provided by the flow of a mixture of 97% oxygen and 3% carbon dioxide. The system is easily and entirely portable. Eleven baboons underwent orthotopic allotransplantation with donor hearts stored by continuous hypothermic (4-10 °C) perfusion for periods of up to 24 hr. Three were electively killed after 2 to 3 days; the remaining eight, immunosuppressed with methylprednisolone and either azathioprine or cyclosporin A, survived to rejection at between 10 and 49 days. Cardiac catheterization performed in six animals 7-14 days after allotransplantation showed virtually normal hemodynamic data. Three more baboons underwent heart excision and storage by hypothermic perfusion for 24 hr, and subsequent othotopic autotransplantation, the circulation of the baboon being maintained in the interim by an allograft. One animal survives 8 months later with hemodynamic data at cardiac catheterization differing little from that obtained before autotransplantation. This perfusion system has subsequently been used to store four human donor hearts prior to heterotopic transplantation. © 1983.