Technique and appropriate equipment are reported which remove blood from the circulation during cardiac systole, thereby reducing intraventricular systolic blood pressure and the work of systolic ejection. Blood is reinjected during ventricular diastole, so that the diastolic blood pressure and coronary blood flow are increased. An electronic circuit enables the phasing of the augmenting systole to be placed accurately in relationship to the QRS complex of the EKG. Application of the technique to experimental heart failure induced by norepinephrine and hemorrhage is illustrated. Cardiac dilatation, elevated end-diastolic pressures, and arterial hypotension are reversed by the use of this technique. In addition, it is possible to supply an unlimited quantity of oxygenated, banked, standard venous blood to the ascending aorta via intra-arterial cannulas. The technique which we have developed overcomes difficulties previously experienced by those who wished to withdraw blood during systole and reinject it during diastole. The size of the pump is adequate to change the blood pressure effectively; the timing of reinjection is such as to accomplish reinjection during the short period of ventricular diastole. Submitted on May 8, 1961