In a group of 72 patients with acute myocardial infarction who underwent a maximal symptom-limited predischarge exercise test in conjunction with radionuclide angiography, 25 (35%) showed greater than 1 mm asymptomatic ST-T-segment depression during exercise. All 25 patients underwent repeated exercise radionuclide angiography 2 days later, 2 h after oral intake of 120 mg diltiazem. Double product was not significantly different before and after diltiazem both at rest and during exercise. Maximal ST-T-segment depression after diltiazem was reduced from 2.4 +/- 0.9 mm to 0.8 +/- 0.6 mm (p less than 0.01). Left ventricular ejection fraction (LVEF) at rest was (before diltiazem) 52.1 +/- 8.9% and (after diltiazem) 55.1 +/- 12.3% (NS). During exercise, LVEF improved after diltiazem from 42.8 +/- 12.1% to 49.1 +/- 10.8% (p less than 0.05). Regional wall motion score (1 = normal, 2 = hypokinetic, 3 = akinetic, 4 = dyskinetic) at rest before diltiazem was 9.9 +/- 2.3 and, after diltiazem, was 9.0 +/- 1.9 (NS). During exercise, regional wall motion score improved after diltiazem from 5.9 +/- 1.3 to 4.2 +/- 1.2 (p less than 0.02). We conclude that diltiazem has acute beneficial effects on asymptomatic ST-T-segment depression and on global and regional left ventricular function in post-infarction patients with silent ischemia.