Background Cardiac MRI is used to measure right ventricular end diastolic volume indexed to body surface area (RVEDVi) and ejection fraction (EF) in the setting of pulmonary insufficiency (PI). There is data describing optimum RVEDVi, in tetralogy of fallot (TOF) patients, to provide a competent pulmonary valve and maintain long term RV function. Pulmonary atresia with intact ventricular septum (PAIVS) and critical pulmonary stenosis (CPS) are congenital heart defects with variable right ventricle (RV) morphology including severe hypoplasia. A subset of these patients undergo initial palliation with right ventricular outflow tract reconstruction to allow for antegrade flow across the pulmonary valve and PI to encourage RV growth over time. There is limited RV volumetric and function data to guide pulmonary valve replacement in this population. The lack of data concerning RV growth in this population may lead to mistimed valve replacement such that RV systolic or diastolic function is permanently compromised. Hypothesis: RVEDVi growth will be different between patients with TOF and PAIVS/CPS; and systolic function will be decreased at equivalent volumes in the PAIVS/ critical PS group.