Pulmonary valve replacement (PVR) in patients with repaired tetralogy of Fallot (rTOF-TAP) is often based on cardiac MRI (CMR) right ventricular (RV) volumes indexed to body surface area (BSA). Weight extremes result in increased patient morbidity and affect indexed measurements. We hypothesized that patients with rTOF-TAP at extremes of weight have (1) over- or underestimated indexed volumes and (2) altered parameters of cardiac function. CMRs in patients with rTOF-TAP were retrospectively reviewed; analysis included right and left ventricular (LV) volumes and ejection fractions (EF) and peak global LV circumferential strain (ε _cc) from myocardial tagged images. Indexed volumes were recalculated using ideal BSA. Weight categories were assigned: underweight, appropriate weight, overweight, and obese. Linear regression models with weight category, spline of age, and gender were created to assess the association of weight and parameters of volume and function. When RV volumes were corrected for ideal BSA, 11 (31%) additional overweight and obese patients met published criteria for PVR and 3 (38%) underweight patients no longer met criteria. Obese and overweight patients had larger absolute LV and RV diastolic volumes, but no difference in volumes indexed to ideal BSA. Modeling demonstrated no difference in LVEF or RVEF by weight categories but significant differences in global LV ε _cc. Extremes of body weight may result in inappropriate timing of PVR. Extremes of weight lead to abnormalities in global LV ε _cc. Although clinical implications of abnormal ε _cc are unclear, these patients may be at higher risk for early ventricular dysfunction.