The addition of enoximone, a phosphodiesterase inhibitor, to adrenergic agents has been found useful in increasing cardiac output in severe heart failure. In one study of 13 patients in cardiogenic shock already receiving adrenergic support, enoximone was administered as a bolus of 0.5 mg/kg over 20 minutes. Pulmonary artery occlusion pressure decreased significantly from 21.7 +/- 5.8 mm Hg to 19.8 +/- 6.0 mm Hg (P less than 0.01) and cardiac index increased markedly. A second study investigated the effects of the addition of small boluses of enoximone to adrenergic agents in low flow states associated with heart failure (n = 8) or postoperative states after cardiac surgery (n = 10). Each of the 18 patients was treated with dobutamine; 12 patients were also treated with dopamine and 4 with noradrenaline. Enoximone was administered as small but increasing intravenous boluses. No significant change in mean arterial pressure was observed, but on 0.5 mg/kg of enoximone pulmonary artery occlusion pressure decreased significantly from 24.6 +/- 8.7 mm Hg to 19.4 +/- 9.9 mm Hg (heart failure) and from 18.2 +/- 3.3 mm Hg to 15.3 +/- 3.8 mm Hg (cardiac surgery) after the initial dose of 0.125 mg/kg. Cardiac index increased markedly after enoximone, 0.25 mg/kg. These changes were significant after the initial dose of 0.125 mg/kg. Thus, the addition of even small doses of enoximone to adrenergic agents can markedly increase cardiac index without significant effect on arterial pressure in medical or surgical cardiac patients.