OBJECTIVE: To examine the authors' hypothesis that during the cardiopulmonary bypass (CPB) in children, the inferior vena cava cannula tip placed proximal to the right hepatic vein orifice would produce a higher venous drainage compared with that placed distally. DESIGN: A prospective, randomized, controlled, double-blind study. SETTING: Single university hospital. PARTICIPANTS: Thirty-two patients aged <6years, scheduled for elective cardiac surgery using CPB for congenital heart disease. INTERVENTIONS: Participants were randomized to 2 groups: the proximal group with the cannula tip placed proximally within 1cm of the right hepatic vein orifice and the distal group with the cannula placed distally within 1cm of the right hepatic vein orifice. MEASUREMENTS AND MAIN RESULTS: The primary outcome of this study was the perfusion flow rate at the time of establishment of total CPB with cardioplegia. The authors initially planned to enroll 60 patients, but before reaching the target sample size, the authors terminated this study owing to patient safety, and 18 patients in the proximal group and 14 patients in the distal group finally were analyzed. No significant differences in patient characteristics were observed between the 2 groups. The mean perfusion flow rate in the proximal group was significantly greater (2.55 ± 0.27 L/min/m2) than that in the distal group (2.37 ± 0.20 L/min/m2, p = 0.04). CONCLUSION: The inferior vena cava cannula tip placed in the proximal position was clinically superior, compared with a distal placement, in producing higher perfusion flow in children.