Twenty-nine patients have undergone the Senning operation for repair of dextro-transposition of the great arteries (TGA) since 1979 at St. Louis Children's Hospital. The early mortality has been comparable to that reported for the Mustard operation (10%). Electrocardiograms (ECGs) following the Senning operation reveal abnormalities similar to those noted after the Mustard operation; 63% of survivors were in normal sinus rhythm 1 week postoperatively, and 86% demonstrated normal sinus rhythm at a mean of 15 months after operation. Twenty-four hour ambulatory monitoring revealed normal sinus rhythm in 35% and occasional premature atrial or ventricular contractions in another 30%. No cases of sudden unexpected death have been noted, and no pacemakers have been inserted. Possible mechanisms for rhythm disturbances following venous transposition operations are discussed.