The effects of digitalis glycosides on myocardial oxygen supply and demand are of particular interest in the presence of obstructive coronary artery disease, but have not been measured previously in man. We assessed the effects of ouabain (0.015 mg/kg body weight) on hemodynamic, volumetric, and metabolic parameters in 11 patients with severe chronic coronary artery disease without clinical congestive heart failure. Because the protocol was long and involved interventions which might affect the determinations, we also studied in nine patients using an identical protocol except that ouabain administration was omitted. Left ventricular end-diastolic pressure and left ventricular end-diastolic volume fell in each patient given ouabain, even though they were initially elevated in only two patients. Left ventricular end-diastolic pressure fell from 11.5+/-1.4 (mean+/-SE) to 5.6+/-0.9 mm Hg (P less than 0.001) and left ventricular end-diastolic volume fell from 100+/-17 to 82+/-12 ml/m2 (P less than 0.01) 1 h after ouabain infusion was completed. The maximum velocity of contractile element shortening increased from 1.68+/-0.11 ml/s to 2.18+/-0.21 muscle-lengths/s (P less than 0.05) and is consistent with an increase in contractility. No significant change in these parameters occurred in the control patients. No significant change in myocardial oxygen consumption occurred after ouabain administration but this may be related to a greater decrease in mean arterial pressure in the ouabain patients than in the control patients. We conclude that in patients with chronic coronary artery disease who are not in clinical congestive heart failure left ventricular end-diastolic volume falls after ouabain administration even when it is initially normal. Though this fall would be associated with a decrease in wall tension, and, therefore, of myocardial oxygen consumption, it may not be of sufficient magnitude to prevent a net increase in myocardial oxygen consumption. Nevertheless, compensatory mechanisms prevent a deterioration of resting myocardial metabolism.