Catheter-induced ventricular ectopy can limit assessment of contractility or anatomy. We compared the incidence of ventricular ectopy in infants and children undergoing left ventriculography using a 4F Halo catheter or a 4F pigtail catheter. For each group, 17 patients had 19 ventriculograms. Iopamidol 76% was used for each study. There was no statistical difference between the Halo and pigtail groups (mean+/-SEM) for age (16.2+/-3.8 vs. 12.9+/-1.8 mo), weight(8.1+/-1.0 vs. 8.0+/-0.7 kg), gender, left ventricular end diastolic pressure (9.6+/-1.1 vs. 9.8+/-1.3 mm Hg), catheter location in the ventricle, or volume of contrast (1.31+/-0.06 vs. 1.35+/-0.06 cc/kg). The Halo group had a more rapid injection rate (1.42+/-0.15 vs. 0.99+/-0.10 cc/kg/sec, P< 0.02). The Halo group had a lower overall incidence of ventricular ectopy (3 vs. 13 studies, P < 0.001), ventricular ectopy >1 beat (1 vs. 10 studies, P < 0.002), and ventricular couplets or tachycardia (1 vs. 9 studies, P < 0.008). The 4F Halo catheter is associated with less ventricular ectopy than a 4F pigtail catheter and should be considered for use during pediatric catheterization.