Pulmonary artery architecture and symmetry after palliative operations for hypoplastic left heart syndrome may affect subsequent suitability for a modified Fontan operation. Two-dimensional echocardiography was used to measure pulmonary artery diameter and assess symmetry after two types of systemic-pulmonary artery shunts: modified right Blalock-Taussig shunt (14 patients) and central shunt (from underside of aortic arch gusset to pulmonary artery confluence) (14 patients). Age, weight, preoperative diameter of right and left pulmonary arteries (proximal, middle, and distal segments), and mean interval between preoperative and postoperative echocardiographic studies (20.2 +/- 4.4 days in the Blalock shunt group; 19.1 +/- 6.8 days in the central shunt group) were similar. Early postoperatively, patients with a Blalock shunt showed a significant decrease in the diameter of all pulmonary artery segments except the distal right pulmonary artery. The diameters tapered from distal right to distal left pulmonary artery in this group. Patients with the central shunt had a significant decrease in the diameter of all pulmonary artery segments. There were no significant differences when cross comparisons were made of the various pulmonary arterial segments in patients after a central shunt. Similar findings persisted in 19 patients from both groups who had a late postoperative echocardiogram (mean interval between studies = 271 days in the group of 10 patients with Blalock shunt and 167 days in the group of nine patients with a central shunt). In conclusion, the central shunt preserves pulmonary artery symmetry, which may be important in candidates for the Fontan operation in infancy.