Seventy three infants who underwent neonatal anatomical correction for transposition of the great arteries with or without a ventricular septal defect were reviewed for evidence of conduction and rhythm abnormalities on preoperative and postoperative 12 lead electrocardiograms and during 24 hour Holter monitoring. There was a partial right bundle branch block pattern in 47% (29/62) of all patients and in 60% (24/40) of those with simple transposition. Complete right bundle branch block was noted in 21% including 5% with simple transposition. Holter monitoring showed sinus rhythm in all patients except three: one had episodes of supraventricular tachycardia, another an intermittent second degree heart block, and a third a complete heart block. Atrial extrasystoles were noted in 47% (29/62) of patients but were frequent in only three patients. Occasional unifocal ventricular extrasystoles were encountered in 37% (23/62) of patients and were frequent in a further 3% (2/62). Only one patient (2%) developed multifocal ventricular extrasystoles. The frequency of important cardiac arrhythmias after neonatal anatomical correction of transposition of the great arteries was 5%, significantly less than that reported after atrial inflow diversion for the same malformation.