T he hemi-Fontan procedure has been proposed as an alternative to the bidirectional Glenn procedure in the first stage of the Fontan operation.1*2 In the hemiFontan operation, an atriopulmonary patch directs superior vena caval blood flow into both pulmonary arteries and the inferior vena caval flow into the ventricle. The hemi-Fontan procedure involves atria1 suture lines, which can potentially affect atria1 conduction and cause arrhythmias. Our surgical experience with the hemiFontan has been reported.2 Here, we report the early effects of the hemi-Fontan on the electrocardiogram and arrhythmias after the hemi-Fontan. Between August 1989 and May 1992,21 children (11 boys and 10 girls, aged 4 months to 5 years [median 11 months]), underwent the hemi-Fontan procedure at our hospital. The underlying cardiac defect was double-inlet left ventricle in 6, hypoplastic left heart syndrome in 5, pulmonary valve atresia with intact ventricular septum in 4, mitral atresia in 3 and complex double-outlet right ventricle in 3. All but 3 had had previous palliative procedures that were modified Blalock-Taussig shunt in 6, pulmonary artery banding in 5, stage 1 Norwood operation in 5, central shunt (a tube graft between the ascending aorta and the pulmonary trunk) in 3, coarctation of the aorta repair in 3, pulmonary artery reconstruction in 2, Blalock-Hanlon atria1 septectomy in 1 and Damus-Kaye-Stansel operation in 1. Before hemi-Fontan, no patient had clinical or electrocardiographic features of arrhythmia. After surgery 2 patients died, both of hemodynamic reasons. Atria1 JEutter occurred in the early postoperative period in 1 patient and recurred later in the same patient. Therapy for this patient was begun with amiodarone and is well controlled. Another had an episode of sustained ventricular tachycardia in the early postoperative period that responded to intravenous lidocaine, and did not reCUK The electrocardiographic results are summarized in Table I. All electrocardiograms showed sinus rhythm. The P-wave axis and PR interval were not sigr$cantly di$erent when compared between preoperative, early postoperative (~30 days) and late postoperative (followup of 5 to 33 months, mean 20) electrocardiograms. Pwave amplitude, however, decreased signijcantly in the early postoperative period. The late postoperative electrocardiogram showed some increase in P-wave amplitude compared with the early postoperative electrocardiogram but was still diminished compared to the preoperative electrocardiogram. No patient had fragmented P waves (defined as >2 upward dejections in