Background: Sildenafil is widely known as a strong pulmonary vasodilator by increasing the intracellular cGMP concentration through inhibition of phosphodiesterase 5. The benefit of oral sildenfil treatment for persistent pulmonary hypertension (PH) early after congenital cardiac surgery was assessed. Methods: After admission to the intensive care unit, sildenafil was administered at a starting dose of 0.5 mg/kg. With careful monitoring hemodynamics, the dose of sildenafil was increased stepwise by 0.5 mg/kg every 4 to 6hours up to a maximum dose of 2.0 mg/kg. After successful weaning from ventilator and other vasodilators, sildenafil was gradually discontinued during the next 5 to 7 days. Medical records of 90 cases were retrospectively reviewed. Results: Age distribution; <1 month: 25, 1 to less than 6 months: 29, 6 to less than 12months: 17, 1 to 3 years: 8, 4 to 9 years: 9, >10 years: 2. Operations; VSD closure: 16, arterial switch: 30, truncus repair: 10, complete AVSD repair: 10, TAPVD repair: 6, ASD+VSD closure: 2, other open heart: 16. Concomitant inhaled nitrous oxide treatment: 64. Changes in pulmonary arterial pressure (monitored in 26 cases); decreased: 20, unchanged: 5, elevated: 1. Bosentan was added in 2 cases with persistent symptoms due to PH despite sildenafil treatment. Modest oxygen desaturation after sildenafil administration: 7. No ‘rebound’ pulmonary hypertension after sildenafil discontinuation and no significant adverse events during sildenafil treatment. Conclusions: Our results suggest that oral sildenafil treatment is a safe and effective alternate for persistent PH after congenital heart surgery in children.