In the search for any deleterious hemodynamic effects of the acute administration of intravenous diltiazem (0.25 mg/kg), in patients on beta blockers, studies were performed in two comparable groups of eight patients with chronic coronary heart disease without clinical signs of heart failure. In the first group, with no previous treatment, the only significant variations observed were a decrease in systemic vascular resistance (p less than 0.01) and an increase in cardiac index (p less than 0.01), which were noted only at 5 minutes. In the second group, receiving long-term oral doses of 120 to 240 mg/day of propranolol, at 5 minutes, despite a slight decrease in peak positive first derivative of left ventricular pressure (p less than 0.05), cardiac index and systolic index increased (p less than 0.05 and p less than 0.01) with decreases in systemic vascular resistance (p less than 0.01) and mean blood pressure (p less than 0.05); at 15 minutes, systemic vascular resistance was still decreased (p less than 0.05) and cardiac index and systolic index were still increased (p less than 0.05). In conclusion, intravenous administration of diltiazem (0.25 mg/kg) to patients with chronic coronary heart disease and no evidence of congestive heart failure, who were receiving propranolol, was safe and prevented, in these patients, the potential deleterious effects of beta blockers, that is, increased peripheral vascular resistance and decreased cardiac output.