Since there are limited studies concerning the hemodynamic effects of verapamil in pediatric patients, cardiovascular effects of clinical doses (100 or 300 μ/kg) of verapamil, given as a 2-min intravenous infusion, were examined in sodium pentobarbital anesthetized swine, aged 1 day (n=15) and 2 wk (n=18). Aortic and left ventricular pressures, index of left ventricular contractility, heart rate, and phasic superior mesenteric, renal, and femoral arterial flows were recorded; mean aortic pressure and vascular resistances were calculated. Maximum changes in cardiovascular function (mean %? ± SEM) occurred at the end of the infusion. Mean aortic pressure and index of left ventricular contractility decreased in all animals; responses were larger in magnitude with the higher dose. By 30 min after infusion of 300 μ/kg verapamil had ended, mean aortic pressure in both 1 day and 2 wk olds and index of left ventricular contractility and femoral flow in 1 day olds were still decreased. During infusion of verapamil, heart rate decreased (—11.6 ± 2.9) to the high dose in 1 day olds but increased (+6.4 ± 2.7) to 100 and 300 μ/kg verapamil in 2 wk olds. After infusion of 300 μ/kg verapamil ended, heart rate decreased and reached the nadir (—10.0 ± 2.9) by 10 min in 2 wk olds. Decreases in renal resistance (—7.6 ± 1.7) were not dose dependent while superior mesenteric resistance decreased (—12.9 ± 2.7) only to low dose verapamil in 2 wk olds. In 1 day olds decreases in renal and superior mesenteric resistance were not sustained throughout the infusion. The results indicate that verapamil has both age- and dose-dependent cardiovascular effects in newborn swine and suggest that verapamil be used with caution in infants.