In the present study, we have examined whether increased N-ANP (N-terminal pro-ANP) levels before and after surgery in patients with ASD (atrial septal defect) along with echocardiographic findings provide a better insight into the pathophysiology and increased morbidity and mortality following corrective surgery. Eighteen adult ASD patients (>20 years of age; six male and 12 female) with shunts ( Q p / Q s ≥2, where Q p / Q s is the pulmonary blood flow/systemic blood flow) had complete echocardiographic, clinical and laboratory parameters evaluated before and 6 months after surgery. Eight age- and sex-matched individuals (three male and five female) were enrolled as a control group. Blood samples for N-ANP analysis were obtained in both groups. N-ANP levels in the peripheral blood sample from ASD patients before surgery were significantly higher than those in the control group. In patients with ASD, mean N-ANP levels obtained from the pulmonary artery were significantly higher than that obtained from the peripheral vein. RA (right atrial) area, adjusted for body surface area, and RA long-axis and short-axis measurements were significantly higher in the patient group than the control group. N-ANP was correlated significantly with these parameters. Following corrective surgery, N-ANP values and RA area, RA long-axis and short-axis normalization decreased significantly and were accompanied by a decrease in systolic mean pulmonary artery pressure. N-ANP levels were normalized following septal closure in most patients, except in those with atrial fibrillation attacks following corrective surgery. In conclusion, we have shown correlations among variables indicating changes in the architecture of the right atrium along with temporal changes in ANP providing insights into the pathophysiology of post-operative atrial arrhythmias.