Postoperative data were obtained from 18 patients with partially obstructed right ventricular (RV) to pulmonary artery (PA) conduits, who were studied 1 to 9 years following a Rastelli operation. Age at operation was 1 to 8 months in seven patients (group I: infant group) and 2 to 9 years in the remaining 11 patients (group II: childhood group). The diagnosis was pulmonary atresia in eight patients, truncus arteriosus in seven, and transposition of the great arteries with ventricular septal defect and pulmonary stenosis in three. Porcine-valved conduits were inserted in 17 patients and an aortic homograft in one. All but seven patients were free of symptoms at the time of postoperative study. Neither peak RV pressures nor RV to PA gradients were different between groups. RV ejection fraction (EF) was decreased in group II (0.43 +/- 0.11) but was normal (0.60 +/- 0.10) in group I. In addition, there was a significant inverse relationship between RVEF and age at repair (r = 0.714; p less than 0.005). RV end-diastolic volume (EDV) was normal or increased in all patients and did not differ between the two groups. Left ventricular (LV) ejection fraction was also decreased in the older group (0.56 +/- 0.10 vs 0.68 +/- 0.08; p less than 0.05), and there was a decrease in RVEF and/or LVEF from pre- to postoperative studies in one of six group I patients compared with four of five group II patients.(ABSTRACT TRUNCATED AT 250 WORDS)