Balloon atrial septostomy is an accepted method for palliation of certain types of congenital heart disease. However, malposition of the balloon may lead to cardiac perforation, avulsion of an atrioventricular valve, or laceration of the systemic or pulmonary veins. Inasmuch as single-phase fluoroscopy may not identify balloon position correctly and as biplane fluoroscopy adds significant radiation exposure, two-dimensional echocardiography has been used to assist in balloon atrial septostomy in ten infants. The catheter is advanced from the inferior vena cava to the right atrium across the foramen ovale to the left atrium with the echo transducer in the subxiphoid position. The balloon is inflated and its position within the left atrium is confirmed by echo. The catheter is withdrawn according to the technique of Rashkind. Withdrawal is halted when the balloon traverses the atrial septum. Adequate septostomy is indicated on echo by a defect at least 5 mm in diameter and by flapping of the inferior rim of the atrial septum. There were no complications using this technique and a clinically adequate septostomy was achieved in each patient. Two-dimensional echocardiography-assisted balloon atrial septostomy minimizes risk of complications and decreases exposure to ionizing radiation.