To evaluate the hemodynamic effects of the first oral administration of enalapril maleate, a long-acting ACE-inhibitor, in the early phase of an acute uncomplicated myocardial infarction, we studied 15 patients, in Killip class I or II, within 72 hours from the onset of symptoms. Hemodynamic measurements were obtained by a triple lumen 7 F Swan-Ganz catheter, inserted into the pulmonary artery, under control conditions and 2, 4, 6, 8 and 12 hours after 10 mg (15 patients) and 20 mg (11 patients) of the drug. Ten milligrams of enalapril reduced systolic and mean arterial blood pressure (from 118 +/- 17 to 111 +/- 18 mmHg, p < .05, and from 92 +/- 12 to 83 +/- 12 mmHg, p < .01, respectively), with a maximum effect after 4 hours from administration. Heart rate and vascular resistances showed an insignificant trend toward reduction, and no changes were observed in left ventricular systolic work index, right and left ventricular filling pressures or cardiac index. Hemodynamic changes induced by 20 mg of the drug, in a smaller group of patients, had a similar trend, which did not reach a statistical significance. In conclusion, in patients with acute uncomplicated myocardial infarction, a single oral dose of enalapril maleate is safe and well tolerated, does not induce severe hypotension, and produces potentially beneficial changes in hemodynamics.