This study was performed to assess changes in pulmonary function test (PFT) and pulmonary outcome after transcatheter closure of atrial septal defect (ASD) in pediatric patients. A total 55 pediatric patients undergoing transcatheter ASD closure received PFT at baseline (day before ASD closure), and at 3 days and 6 months after procedure. Forced vital capacity (FVC), forced expired volume in 1 sec (FEV(1)), FEV(1) to FVC ratio (FEV(1)/FVC), peak expiratory flow (PEF), and mean forced expiratory flow during the middle half of FVC (FEF(25-75)) were measured. Individually, subjects were classified by spirometry as normal, obstructive or restrictive, to evaluate the effect of transcatheter closure on pulmonary outcome. These 55 children had significantly reduced mean PEF and FEF(25-75) (84 +/- 24%, P = 0.040 and 76 +/- 22%, P = 0.010, respectively) at baseline, with FEF(25-75) reduced significantly at 3 days and 6 months (78 +/- 24%, P = 0.010 and 81 +/- 24%, P = 0.040, respectively) after transcatheter closure. Six months after transcatheter closure of ASD, significant improvement was observed in mean FVC (94 +/- 19% vs. 98 +/- 15%, P = 0.034) and FEV(1) (90 +/- 20% vs. 96 +/- 19%, P = 0.008). Assessed individually, better pulmonary outcome was found in patients without pulmonary hypertension (PH) (chi(2) = 8.333, P = 0.044). PFT disturbance was observed in significant flow limitation in the peripheral airway of ASD patients. Improved PFT was found after transcatheter closure and better pulmonary outcome was observed in patients without PH. ASD children need monitoring pulmonary function and should receive transcatheter closure before PH develops.