Serial changes of electrocardiograms (ECG) could be used to assess their clinical features in atrial septal defects (ASD) after transcatheter closure together with other clinical parameters. We retrospectively studied 100 ASD patients who underwent transcatheter closure. Complications of persistent atrial fibrillation occurred in five ASD patients, and they were excluded. We divided the other 95 patients according to PQ intervals before closure (normal: < 200 ms, n = 51; prolonged: ≥ 200 ms, n = 44) to evaluate their clinical characteristics and parameters such as echocardiography, chest X-rays, and brain natriuretic protein (BNP) levels. Individuals in the prolonged PQ group were significantly older, had higher incidences of paroxysmal atrial fibrillation (PAF) and heart failure (HF) treated with more β-blockers and diuretics, and with a higher tendency of NYHA functional classification and BNP levels than the normal PQ group. The prolonged PQ group also had a significantly higher incidence of complete right bundle branch block, wider QRS intervals, and larger cardiothoracic ratios in chest X-rays accompanied by larger right atrial-areas and larger left atrial dimensions in echocardiograms. Furthermore, the prolonged PQ intervals with less PQ interval shortening after transcatheter closure revealed that the patients were the oldest at the time of closures and showed less structural normalization of the right heart and left atrium after ASD closure. PAF and HF also occurred more frequently in this subgroup. These results suggested that the ASD patients with prolonged PQ intervals with less PQ shortening were accompanied by more advanced clinical conditions. Together with other clinical parameters, detailed analyses of ECG and their changes after closure could elucidate the clinical characteristics and status of ASD patients with transcatheter closure and were useful for predicting structural normalization after transcatheter closure.