We scrutinized the preoperative electrocardiographic and hemodynamic findings in adult atrial septal defects older than 15 years, and then followed up the postoperative electrocardiographic changes sequentially. In preoperative electrocardiographs, the mean PR interval [0.17 sec] was prolonged than normal adults [M;0.13,F;0.15], and the mean QRS axis [93.1*] was deviated to rightward than normal [M;63.7*,F;64.4*], and 122 cases of all 159 patients [77.8%] were in RAD quadrant. The QRS morphology was classified into three groups; a] crista supraventricularis hypertrophy, 25 cases, b] right ventricular outflow tract hypertrophy, 89 cases, c] right ventricular hypertrophy, 44 cases, and normal rs pattern, 1 case. Comparing the QP/QS, Pp/Ps, Rp/Rs in these three groups, Qp/Qs increased a] 2.65 to b] 2.97 and decreased b] 2.97 to c] 2.55, Pp/Ps increased a] 0.27 to b] 0.35 to c] 0.44, and Rp/Rs increased a] 0.1 to b] 0.14 to c] 0.2. In comparing the atrial fibrillation with sinus rhythm, the patient`s mean age was increased [26.4 to 45.7], the mean Qp/Qs was decreased [2.97 to 2.7], the mean Pp/Ps was increased [0.35 to 0.46], the mean Rp/Rs increased [0.14 to 0.2], and the QRS morphology was RVOT hypertrophy;7 cases, RVH;2 cases in all 11 cases. Therefore, the atrial fibrillation was appeared in progressed status. Increasing the mean pulmonary arterial pressure, size of the R` wave in Vl lead increased, and the QRS morphology tended to become severe patterns. Postoperatively, the PR interval shortened and QRS axis tended to normal axis quadrant, and size of R` wave decreased sequentially, atrial fibrillation disappeared in 4 cases. Conclusively, by use of the conventional surface electrocardiography, we could anticipate the hemodynamic changes and the prognosis at outpatient department.