OBJECTIVE The phosphodiesterase-5 inhibitor sildenafil was developed for the treatment of pulmonary hypertension. The authors investigated the efficacy and safety of sildenafil in the early postoperative period after mitral valve surgery in patients with pulmonary hypertension. METHODS A double-blind, placebo-controlled randomized trial was performed. METHODS The trial was performed in a single tertiary referral center. METHODS Fifty consecutive patients who experienced pulmonary hypertension and underwent mitral valve surgery. METHODS Patients were randomly assigned to the following 2 groups: 25 patients received 20 mg sildenafil every 8 hours, and the remaining 25 patients received placebo during the same period. Hemodynamic parameters were studied by using a pulmonary artery catheter at baseline and every 6 hours up to 36 hours. RESULTS Patients who received sildenafil showed a decrease in mean pulmonary pressure, from 32 ± 7 mmHg at baseline to 26 ± 3 mmHg after 36 hours, whereas no change was seen in patients who received placebo (mean pulmonary pressure 34 ± 6 mmHg at baseline and 35 ± 5 mmHg after 36 h) (p < 0.001). No significant changes in systemic hemodynamic and oxygenation were observed. Patients who received sildenafil compared with those who received placebo had a median mechanical lung ventilation time of 16 (10-31) hours versus 19 (13-41) hours (p = 0.431), intensive care unit stay of 74 (44-106) hours versus 91 (66-141) hours (p = 0.410), and a total hospitalization stay of 7 (5-10) days versus 11 (7-15) days (p = 0.009). CONCLUSIONS The immediate postoperative administration of sildenafil after mitral valve surgery is safe. Sildenafil demonstrates a favorable decreasing effect on pulmonary vascular pressure without systemic hypotension and ventilation-perfusion mismatch.