There are very few studies in the literature on respiratory system functions and complications of children with an atrial septal defect (ASD). The aim of this study is to investigate the pulmonary functions and pulmonary complications before and after transcatheter closure in children with an ASD. In this study, pulmonary function test parameters of 30 ASD patients between 5 and 18 years of age who were eligible to be treated by transcatheter ASD closure were compared with 30 healthy children. The patients undergoing transcatheter ASD closure received pulmonary function tests (PFT) at baseline (1 day before ASD closure), and 3 months after the procedure. Forced vital capacity (FVC), forced expired volume in 1 s (FEV1), peak expiratory flow, and mean forced expiratory flow during the middle half of FVC were measured. The mean age of the 30 ASD patients was 9.59 +/- 3.1 years; and 20 (66.6%) were female and 10 (33.3%) were male. The mean age of the control group was 10.15 +/- 2.21 years, and 19 (63.3%) were girls and 11 (36.6%) were males. ASD patients had significantly reduced FVC (73.11 +/- 24.6%; 86.05 +/- 26.1; p = 0.001, respectively), and FEV1 (81.34 +/- 26.2% and 99.2 +/- 19.6%; p = 0.001; respectively) at baseline. But significant improvement was observed in FVC values in the 3(rd)-month post-closure comparison of the patient group with the control group (73.11 +/- 24.6%; and 88.36 +/- 14.5%; p = 0.01, respectively); FEV1 values (81.34 +/- 26% and 99.54 +/- 18.2%; p = 0.005, respectively) and mean forced expiratory flow between 25 and 75% of vital capacity (MEF25-75) values (94.6 +/- 33.4% and 124.2 +/- -24.1%; p = 0.01, respectively) were also improved. There was no statistically significant relationship between the PFT measurements at baseline and after closure of the defect and age at transcatheter closure, gender, body height, body weight, ASD diameter, Q (p)/Q (s), right ventricle systolic pressure, or mean pulmonary artery pressure values. At the 3(rd) month of ASD closure, there was no significant difference in the comparison of the PFT values of the patient and control group. Disturbance in the significant flow limitation of the peripheral airway of ASD patients was observed with PFT. Better pulmonary outcomes were observed in ASD patients after transcatheter closure.