Before operation as well as over a mean postoperative period of 8.9 years 222 adults with atrial septal defects underwent a follow-up examination concerning frequency and clinical significance of supraventricular dysrhythmias. Thereby disturbances of the formation of stimuli were found before the operative procedure in 60 patients and after the correction in 115 patients. Disturbances of the sinoatrial and atrioventricular conduction were registered preoperatively in 53 cases and postoperatively in 81 cases. Within these statistically significant increases in particular the significant forms of dysrhythmia elevated after the atrial septal defect closure. Thus the tachycardiac atrial dysrhythmias increased from 7 to 28%, complex arrhythmias even from 2 to 16%. Of dysrhythmias to be taken seriously patients with IAVC and supraventricular defect are significantly more frequently affected than those with interatrial septal defects. Size of the defect, shunt volume and pressure of the pulmonary artery did not show any connections with the frequency of dysrhythmia. On the other hand, when accompanying cardiac anomalies, symptoms of a manifest heart insufficiency were present and at an operation age over 40 years arrhythmias were proved more frequently. The complaints of the patients did not correlate with the endangering, but are imprinted by the haemodynamics and its postoperative normalization. By the established profile of complaints and a decrease of frequency from 76% pre- to only 40% postoperative the patient with atrial septal defect cannot estimate his individual risk and needs an adapted long-term concept for his cardiological care.