Between July 1991 and March 1993, five children (ages 2 to 6 years) with complex congenital heart disease have undergone a new operation for conversion to the Fontan circulation. This procedure combines a bidirectional Glenn shunt with an extracardiac lateral tunnel (ELT) to carry systemic venous return to the pulmonary arteries (PAs). The ELT was constructed so that the circumference consists of Gore-Tex (2/3) and lateral epicardial atrial wall (1/3). The ELT can be performed with all varieties of single ventricle physiology, as in our patients with tricuspid atresia (n = 3), dextrocardia (n = 1), and situs inversus with levocardia (n = 1). PA reconstruction was required in four patients. At follow-up from 1 to 20 months, all patients are in New York Heart Association Class I and in normal sinus rhythm. Postoperative catheterization has revealed low PA pressures (< or = 12 +/- 1 mmHg) and angiography has shown excellent ELT function with brisk flow into the PAs bilaterally. All patients maintain an O2 saturation > 94% on room air. The advantages of this new extracardiac modification of Fontan's operation are: (1) aortic cross-clamping is not usually required; (2) incorporation of lateral atrial wall in ELT allows for growth while permitting construction of a fenestration or adjustable atrial septal defect in high risk patients; (3) absence of atriotomy and intraatrial suture lines may decrease late risk of arrhythmias; (4) early or late baffle leaks cannot occur; (5) intraatrial obstruction from the baffle cannot occur; (6) coronary sinus remains in low pressure atrium; and (7) hydrodynamic benefits of the total cavopulmonary connection are preserved. We recommend this procedure for patients undergoing surgical conversion to the Fontan circulation.