Abstract: An apparatus for perfusing the heart of a patient with oxygenated blood detects the blood pressure at the point of supply, usually the aortic root or a coronary blood vessel, and transmits this pressure to a pressure switch which controls a solenoid valve for recycling blood driven by a roller pump to the oxygenator, or, selectively, through a surge tank and to the point of supply within the patient's vascular system. The surge tank has an air cushion therein for holding essentially constant the pressure at which the blood is supplied to the patient, and, thus, for holding constant the pressure at the point of supply.The system is fail-safe since the pressure switch can be connected to the solenoid so that blood is pumped to the surge tank and thence to the patient in the event of the failure of an electrical connection to the solenoid valve.