Verapamil, a calcium channel blocking drug, terminates supraventricular arrhythmias but may have a negative inotropic effect and produce peripheral vasodilatation and hypotension. We studied the efficacy of intravenous calcium gluconate in reversing or preventing the hypotensive effect of verapamil in 31 patients with atrial tachyarrhythmias. In 21 instances, verapamil was given first, and in 13 calcium was used as pretreatment before the administration of verapamil. Calcium gluconate, when given as pretreatment, prevented the fall in blood pressure induced by verapamil, and when given after verapamil restored blood pressure to control values. The administration of calcium did not alter the antiarrhythmic effect of verapamil.