Atrial arrhythmias are associated with enlarged atrial chambers and an increased duration of the P wave. Repair of atrial defects within the oval fossa is expected to normalize atrial size. Few studies, however, have evaluated electrical and morphological atrial features after repair. Our study was performed to determine if atrial abnormalities exist after surgical closure of such atrial septal defects, and whether early closure improves outcome. We recruited patients who had undergone surgical closure of a defect within the oval fossa, so-called “secundum” atrial septal defects. Electrocardiograms, signal averaged electrocardiograms, and echocardiograms were performed. Two-tailed test and Pearson correlation was utilized for statistical analysis. The population consisted of 20 patients and 27 controls, with the mean age of the patient being 11.25 ± 5.10 years, their age at surgery 6.55 ± 5.10 years, and the time since surgery 4.70 ± 2.61 years. The size of the right (23.88 ± 6.35 ml/m2 versus 18.84 ± 4.43 ml/m2) and left (21.91 ± 12.47 ml/m2 versus 17.72 ± 4.83 ml/m2) atrium were significantly larger in the patients. The duration of the P wave (108 ± 16 ms versus 96 ± 8 ms) and the duration of the PR interval (155 ± 18 ms versus 138 ± 23 ms) were longer. No correlation existed between age or interval since surgery with atrial sizes or measurements of the signal averaged electrocardiogram. We conclude that, despite surgical repair, abnormalities exist in patients with an atrial septal defect. Early surgery does not appear to prevent the atrial abnormalities.