BACKGROUND: Neonates and infants often require extended periods of mechanical ventilation facilitated by sedation and neuromuscular blockade. METHODS: Twenty-three patients aged younger than 2 yr were randomly assigned to receive either cisatracurium or vecuronium infusions postoperatively in a double-blinded fashion after undergoing congenital heart surgery. The infusion was titrated to maintain one twitch of a train-of-four. The times to full spontaneous recovery of train-of-four without fade, extubation, intensive care unit discharge, and hospital discharge were documented after drug discontinuation. Sparse sampling after termination of the infusion and a one-compartment model were used for pharmacokinetic analysis. The Mann-Whitney U test and Student t test were used to compare data between groups. RESULTS: There were no significant differences between groups with respect to demographic data or duration of postoperative neuromuscular blockade infusion. The median recovery time for train-of-four for cisatracurium (30 min) was less than that for vecuronium (180 min) (P < 0.05). Three patients in the vecuronium group had prolonged train-of-four recovery: Two had long elimination half-lives for vecuronium, and one had a high concentration of 3-OH vecuronium. There were no differences in extubation times, intensive care unit stays, or hospital stays between groups. CONCLUSIONS: Our results parallel data from adults demonstrating a markedly shorter recovery of neuromuscular transmission after cisatracurium compared with vecuronium. Decreased clearance of vecuronium and the accumulation of 3-OH vecuronium may contribute to prolonged spontaneous recovery times. Cisatracurium is associated with faster spontaneous recovery of neuromuscular function compared with vecuronium but not with any differences in intermediate outcome measures in neonates and infants.