OBJECTIVE To evaluate the efficacy and safety of intravenous sildenafil for immediate postoperative pulmonary hypertension (PH) in pediatric patients undergoing congenital heart surgery. METHODS A double-blind, multicenter, placebo-controlled, dose-ranging, parallel-group trial was conducted. Patients were randomized to one of three doses of intravenous sildenafil, or placebo, for a minimum of 24 h. RESULTS The study was heavily underpowered. Whereas enrollment of 228 patients (57 per treatment arm) was required to achieve the sample size estimate to detect difference between arms, the sponsor terminated the study after 15 months owing to slow patient accrual. Seventeen patients (median age 5 months) experiencing postoperative PH were randomized and treated, five with placebo and four each with low-, medium-, and high-dose sildenafil. In the first 24 h, 40% of placebo and 17% of sildenafil patients required additional therapy (p = 0.330). Median time to extubation (3 versus 8 days, p = 0.023) and intensive care unit stay (6 versus 15 days, p = 0.008) were shorter for sildenafil patients. Mean ± standard deviation systolic pulmonary artery pressure was reduced with sildenafil (46 ± 11 to 35 ± 6 mmHg, p = 0.027 versus placebo). No adverse events or systemic hypotension were attributed to sildenafil. CONCLUSIONS Intravenous sildenafil reduced pulmonary artery pressure and shortened time to extubation and intensive care unit stay in children with postoperative PH.