Background Mixed pulmonary disease with pulmonary regurgitation (PR) and stenosis (PS) in repaired tetralogy of Fallot (rTOF) can negatively impact ventricular health. Myocardial strain has been shown to be more sensitive at detecting occult ventricular dysfunction compared to right ventricular ejection fraction (RV EF). We hypothesize that rTOF patients with predominant PS will have lower RV global longitudinal strain (RVGLS) prior to and post-transcatheter pulmonary valve replacement (TPVR). Methods A retrospective cohort of rTOF patients who underwent cardiac magnetic resonance (CMR) and cardiac catheterization for right ventricular pressure (RVSP) measurement were analyzed at three time points: before valve implantation, at discharge and within 18 months post-TPVR. Patients were dichotomized into three groups based on RVSP: 0-49%, 50-74%, and >75%. RVGLS and left ventricular (LV) GLS by speckle tracking echocardiography (STE) were obtained from the apical 4-chamber using TomTec software (TOMTEC IS, Germany). Results Forty-eight patients were included. RV EF was not associated with a significant change in RV or LV GLS (p=0.7). RV GLS showed the greatest improvement immediately after valve implantation. Higher pre-implantation RVSP was found to correlate with worse strain (p=0.001). Overall, average RV strain magnitude was higher when pre-implantation RVSP was less than 50% and had greater improvement over the three time points. Higher post-implantation RVSP correlated with lower strain magnitude. Conclusion Patients with significant PS (>50%) may benefit from earlier PVR and not depend solely on RV size and EF. Myocardial strain may be a more sensitive marker of function; however, larger, prospective studies are needed.