BACKGROUND After tetralogy of Fallot (TOF) repair, severe pulmonary insufficiency is known to impair biventricular function. Pulmonary valve replacement (PVR) alleviates symptoms, normalizes right ventricular volumes, and improves ventricular function. Most studies addressing the role of PVR have examined older adolescents or adults. Less is known about the potential benefits of PVR in preadolescents with TOF and significant right ventricular dilatation. METHODS We reviewed the clinical data for all preadolescents (< or = 13 years) with TOF who underwent cardiac magnetic resonance imaging (cMRI) or PVR, or both. Serial cMRI data were analyzed to determine the change in indexed right ventricular end-diastolic volume (RVEDV) and biventricular ventricular ejection fractions. Available cMRI data after PVR were compared with data before PVR. RESULTS During the study period, 101 preadolescents with TOF had cMRI. The median age of complete repair was 6 months (range, 6 days to 3.4 years). The mean RVEDV at the first study was 135 +/- 39 mL/m(2). For 32 with serial cMRI studies, the RVEDV increased at a mean yearly rate of 9 mL/m(2). Ventricular systolic function was impaired in 46 (46%). Forty-two patients underwent PVR at a mean age of 8 +/- 3 years. No hospital deaths occurred, and no pulmonary valve reinterventions have been required. CONCLUSIONS Significant right ventricular dilatation is common in preadolescents after transannular patch repair of TOF. Routine follow-up of this population should incorporate cMRI. Further studies will be needed to determine whether a strategy of early PVR might improve intermediate-term outcome.