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To describe the incidence of QRS prolongation, intraventricular conduction delay (IVCD), and presence of ventricular arrhythmias in patients undergoing the Norwood procedure with subsequent superior cavopulmonary anastomosis. Differences between the modified Blalock-Taussig shunt (BTS) and the right ventricle to pulmonary artery shunt (RV-PA) on these variables were investigated.Eighty-two consecutive patients underwent Norwood palliation with a BTS (n = 41) or a RV-PA (n = 41). Standard 12-lead surface ECGs were retrospectively reviewed at three separate times: (1) prior to the Norwood procedure, (2) immediately post-Norwood procedure, and (3) prior to the superior cavopulmonary anastomosis. Groups were compared at these times for the absolute QRS duration, the change in QRS duration from one time interval to the other, and the number of patients with IVCD. The presence of ventricular rhythm abnormalities requiring treatment at any time was recorded.Immediately after the Norwood procedure, QRS duration was slightly longer and median QRS change slightly larger for the RV-PA than the BTS group (P = 0.04). However, there were no differences in these variables at the time of pre superior cavopulmonary anastomosis. Within both groups, there was a significant increase in median QRS duration over time; from both pre- and post-Norwood to presuperior cavopulmonary anastomosis (P < 0.001).IVCD is common in patients following a Norwood procedure regardless of the type of shunt received. A ventriculotomy had small effects on QRS duration in the short term, but had no effect on the incidence of treatable ventricular rhythm abnormalities.