This electrocardiogram shows right ventricular enlargement and left axis deviation. The characteristic features of right ventricular enlargement demonstrated here include: an rSR' complex and associated ST-T abnormalities in lead V1. Left axis deviation is demonstrated by the predominantly negative QRS complex in II and aVF, with a tall positive complex in lead aVL. First degree A-V block is also present, as evidenced by the prolonged PR interval. These electrocardiographic changes are found in ostium primum atrial setptal defect.