The acute hemodynamic effects of intravenous Diltiazem were studied in 20 pts. with acute myocardial infarction, admitted to Coronary Care Unit within 24 hours from onset of Symptoms--19 men, 1 woman, aged from 46 to 83 years, 14 with anterior myocardial infarction, 6 with inferior myocardial infarction. All, but one, where at the time of their admission to CCU in first Forrester's hemodynamic subset (CI greater than 2.2 L/min/m2, WP less than 18 mmHg); in the last patient WP was 21 mmHg, CI 2.6 L/min/m2. Hemodynamic measurements were performed before (no drugs with hemodynamic effects were allowed during 4-6 hours before the study protocol) and after the administration of Diltiazem, 0,3 mg/kg i.v. administered in 2 min. (bolus) in 12 patients, Group A. In 8 pts--Group B--the bolus was followed by continuous infusion of Diltiazem at the rate of 5 mcg/Kg/min for three hours. The hemodynamic measurements were repeated: in Group A 2-5-30-60-120 min. after the end of the bolus; in the Group B at the same time as Group A, at the end of infusion (180 min) and 60 min after the end of infusion. Diltiazem induced no significant changes of HR, CVP, WP, CI, LVSWI and Triple product, in both groups of pts., at any time. Systolic and diastolic blood pressure decreased significantly (P less than 0.01) only 2 min. after Diltiazem administration (Group A: SBP 125.0 +/- 15.8----114.0 +/- 16.0 mmHg, DBP 85.4 +/- 6.5----76.6 +/- 10.5 mmHg; Group B: SBP 123.0 +/- 20.0----113.0 +/- 11.0 mmHg, DBP 78.1 +/- 7.0----75.0 +/- 4.9 mmHg).(ABSTRACT TRUNCATED AT 250 WORDS)