Since Isoptin increases coronary blood flow in the dog and improves patients with angina pectoris, the drug was studied by coronary cineangiography (Sones' technique) to determine the degree of vasodilatation so produced. When Isoptin, 5 mg. in 2 ml. of solvent, was injected intravenously into five patients with coronary disease and five without coronary disease, there was no change in the size of the main coronary vessels or in the degree of impregnation of the heart muscle, and no new vessels appeared. Isoptin produced a constant decrease in systolic, diastolic and mean blood pressure and a constant increase in heart rate.The clinical improvement in patients taking the drug may be independent of coronary vasodilatation. The drug may act by antagonizing beta-adrenergic effects.