Abstract only Background: Patients with pulmonary atresia with intact ventricular septum (PA/IVS) and critical pulmonary stenosis (CPS) managed to a biventricular circulation may eventually require pulmonary valve replacement (PVR) for pulmonary regurgitation (PR). Right ventricular (RV) remodeling after PVR has been well described in tetralogy of Fallot (TOF); we sought to investigate RV volumetric and functional changes in PA/IVS using CMR. Methods: A retrospective cohort of PA/IVS and CPS patients who underwent PVR at Boston Children’s Hospital from 1995-2021 with CMR before and after PVR was matched 1:3 with TOF patients by age at PVR. Patients with initial intervention >2 weeks of age or 1.5 ventricle circulation were excluded. Median regression modeling accounting for matching was performed with reduction in indexed right ventricular end diastolic volume (RVEDVi) post PVR as the primary outcome, adjusting for covariates including tricuspid regurgitation (TR) and PVR valve size. Results: Twenty PA/IVS or CPS patients (cases) were matched with 60 TOF (controls), with median age at PVR 14 years; at median follow-up 8 years post PVR, 95% were NYHA Class I. Pre-PVR RVEDVi was similar between groups (165 vs 167 ml/m 2 , p=0.7), although cases had higher RV EF (51.4 vs 48.6%, p=0.03), TR fraction (23 vs 9%, p=0.008), and a trend toward lower RV mass; PR fraction, LV volumes and EF were similar. Pre-PVR RV free wall and LV longitudinal strain were similar, although LV circumferential strain was worse in cases (-15.6 vs -17.1, p=0.01). At median 2 years after PVR, RVEDVi was similarly reduced from 166 to 118 ml/m 2 (p=0.73), although cases had higher RV EF (52.3% vs 46.9%, p=0.007) with less reduction in indexed RV mass (Δ4.5 vs 9.6 g/m 2 , p=0.02); LV volumes and EF were similar. Post PVR, RV and LV longitudinal strain remained unchanged both within and between groups; LV circumferential strain was similar post PVR and remained lower in cases vs controls. Conclusion: Patients with PA/IVS after PVR demonstrate similar RV remodeling to TOF patients, with lesser reduction in RV mass and comparatively better post RV EF. CMR strain imaging found no significant pre-post differences in RV or LV systolic parameters. Further investigation is needed to evaluate for changes in diastolic parameters.