Verapamil was given to 16 consecutive patients with multifocal atrial tachycardia. Intravenous verapamil was administered at rate of up to 1 mg/min while heart rate and systolic blood pressure were being monitored. The final 5 patients reveived 1 g of intravenous calcium gluconate 5 minutes before treatment with verapamil; the first 11 received no calcium. The mean heart rate decreased by 21% from 129 to 101 beats/min, a difference of 28,95% confidence interval (CI), 18 to 38 (p<0.0005 by t-test), after a mean of 22±13 minutes from the start of verapamil administration. The mean verapamil dose was 17±7 mg (6 to 30 mg). Sinus rhythm was restored in 8 patients. Pretreatment with calcium did not block the effect of verapamil on heart rate (27% decrease with calcium compared with 19% decrease without calcium, a difference of 8%, 95% CI -7 to 23; p=0.29) but minimized the decrease in systolic pressure (11% decrease with calcium compared with 27% decrease without calcium, a difference of 16%, 95% CI, 7 to 27; p<0.01). verapamil caused transient asymptomatic hypotension in 1 patient. Arterial blood gases were unchanged by verapamil. Thus, verapamil is safe and effective therapy for multifocal atrial tachycardia, consistently slowing the heart rate and often restoring sinus rhythm. Calcium pretreatment may reduce drug-induced hypotension without preventing the antiarrhythmic effect.