To determine the optimal left ventricular filling pressure (LAP) after cardiopulmonary bypass (CPB) left ventricular function curves were constructed in ten patients with coronary heart disease, seven with aortic stenosis and normal left ventricular filling pressures (NLVFP), eight with aortic stenosis and pathologic elevated left ventricular filling pressure (ELVFP), and nine with mitral valve disease, cardiac index = CI, stroke index = SVI, left ventricular stroke work index = LVSWI were plotted against left atrial pressure = LAP and correlated with myocardial lactate extraction. After CPB, CI and LVSWI increased 52 to 53% and 50 to 80%, respectively, in the patients with NLVFP. In the patients with preoperatively ELVFP SVI did not increase significantly with increasing LAP, resulting in no augmentation of CI and LVSWI. Total systemic resistance increased in these patients, and myocardial lactate metabolism shifted to production in the patients with severe aortic stenosis. Thus, the results show that SVI, CI and LVSWI cannot be augmented by increasing LAP above 15 mm Hg if preoperative left ventricular function is already impaired. Elevation of LAP above 20 mm Hg can induce myocardial ischemia and cause low cardiac output with increased peripheral vascular resistance.