Objectives; Congenital heart disease (CHD) with pulmonary arterial hypertension (PAH) has somewhat high risk of postoperative morbidity and mortality. Inhaled iloprost has been approved to be effective in the treatment of PAH. We assessed the efficacy and safety of inhaled iloprost treatment in cases of CHD with PAH before and after operation. Methods ; Total 20 patients who had VSD or ASD with PAH showing bidirectional shunt or right ventricular pressure(RVP) estimated more than 60% of systemic pressure in the preoperative echocardiogram were enrolled. 10 patients (Group I) were treated with inhaled iloprost before (mean 7.4 days) and after (mean 5.8 days) operation. 10 patients (Group II) were not given. We investigated subcutaneous oxygen saturation (SaO2), RVP in the echocardiogram, and postoperative clinical course like duration of ventilator application, inotropic support, ICU stay, and chest tube drainage. Results; Mean age (13.6 짹 16.5 vs 10.3 짹 12.7, P=0.3) and weight (26.1 짹 22.3 vs 20.8 짹 16.2, P=0.44) in both groups were not different statistically. No perioperative mortality was encountered. There were increased SaO2 (92.4짹2.9% to 96.8짹2.4%, P<0.005) and decreased estimated RVP (84.6짹18.1 mmHg to 74.9짹14.2 mmHg, P=0.13) with preoperative use of inhaled iloprost in Group I. In the postoperative clinical course, Group I showed shorter duration in days compared to Group II, statistically insignificant though: mechanical ventilation (1.5짹1.1 vs 2.2 짹 1.5, P=0.14), inotropic support (3.4 짹 1.9 vs 4.3 짹 1.4, P=0.13), ICU stay (3.5 짹 1.9 vs 4.8 짹 1.6, P=0.07) and chest tube drainage (4.0 짹 0.9 vs 5.2 짹 1.9, P=0.057). Conclusion; Our study represented that perioperative medical intervention with inhaled iloprost was effective to reduce pulmonary arterial pressure and to improve postoperative clinical course in congenital heart diseases with pulmonary hypertension.