Abstract: The present invention is a cardiac-assist device and technique used to maintain a patient's cardiac output when normal cardiac output is insufficient. Blood is removed from a selected ventricle using an arterial or venous side approach. The use of a right side approach reduces the amount of work required and reduces the number of foreign objects present within the left side of the heart and associated blood transferring conduits. The device of the invention includes a flexible catheter positionable within the patient's body. An external assist mechanism connected to one end of the flexible catheter receives blood from the arterial circulation and includes a pumping membrane. A flexible cannula is connected for reinfusing blood. A control console is provided for alternately supplying vacuum and pressure to the pumping membrane. A synchronizing means varies inflation and deflation in synchrony with the cardiac cycle of a patient.