Electrocardiograms from 30 patients with congenital atrial septal defect operated upon in adult age were analyzed. One of frequent variants of QRS configuration in standard leads was SIqIII type. It was observed in 50% of patients. Most frequent (in 67% of patients) variants of QRS configuration in lead V1 were rSr' and rSR'. Signs of right ventricular hypertrophy were most often found in a group of patients with high pulmonary hypertension. Changes of terminal portion of ventricular complex such as negative or biphasic T waves were found in 29 of 30 patients (in 63% of cases these changes were localized in leads V1-V3).