We report our experience with balloon atrial septostomy under two-dimensional echocardiographic guidance only in 44 newborn patients (39 patients with transposition of the great arteries) who needed creation of an interatrial communication. Using standard echocardiographic projections septostomy with creation of large atrial septal defects was easy in 41 newborns. In 3 patients insertion of a large Eustachian valve at the interatrial septum prevented adequate pull-throughs with larger balloon sizes. No serious complications due to the procedure were noted. Balloon atrial septostomy under two-dimensional echocardiographic control is a quick, effective and safe method which can be performed on the intensive care unit.