The effects of oral diltiazem (120 mg), propranolol (100 mg), and placebo on exercise performance and left ventricular function were compared before and during symptom-limited supine bicycle exercise by means of multigated radionuclide ventriculography in 12 patients with documented, symptomatic coronary artery disease; a double-blind, randomized crossover protocol was used. Diltiazem increased ejection fraction (EF) at submaximal exercise (+7.0 absolute percentage points, p less than 0.02) and maximal exercise (+8.1 percentage points, p less than 0.01). Exercise EF was increased by 13.6 percentage points (p less than 0.02) in patients with decreased ventricular function (resting EF less than 50%). Propranolol had no effect on exercise EF at any stage, even when patients with EF less than 50% were excluded. The increase in total exercise time was significant after diltiazem (+27%, p less than 0.01) but not after propranolol (+16%, p = NS). As expected, propranolol decreased both resting (-9 bpm, p less than 0.01) and exercise heart rates (-27 bpm, p less than 0.001), whereas diltiazem had no significant effect. Propranolol decreased resting diastolic blood pressure (-8 mm Hg, p less than 0.02), exercise systolic (-27 mm Hg, p less than 0.001) and diastolic (-9 mm Hg, p less than 0.01) blood pressures, and rest (p less than 0.01) and exercise (p less than 0.001) double product. Diltiazem decreased resting systolic blood pressure (-9 mm Hg, p less than 0.01) and both resting (-8 mm Hg, p less than 0.001) and exercise (-9 mm Hg, p less than 0.01) diastolic blood pressures.(ABSTRACT TRUNCATED AT 250 WORDS)