BACKGROUND Pulmonary regurgitation leading to right ventricular enlargement may occur after repaired tetralogy of Fallot (rTOF) or balloon dilation for pulmonary valve stenosis. Cardiac magnetic resonance imaging (CMR) guidelines to identify the timing of valve replacement in rTOF are not necessarily applicable to isolated pulmonary regurgitation. This study aims to compare deformation parameters of isolated pulmonary regurgitation and rTOF at comparable right ventricular volume loads. METHODS Adopting a quantitative retrospective analytic framework, CMR was performed in 44 patients (0-30 years), 22 in each of the isolated pulmonary regurgitation and rTOF study arms, matched for age (±12 months), and Right ventricular end-diastolic volume z-score (±1). Right ventricular longitudinal strain/strain rate and circumferential strain/strain rate were measured. Comparisons between groups were analysed using two-tailed T-tests and one-way ANOVA. RESULTS Both groups showed predominance of longitudinal over circumferential strain. Circumferential strain was significantly greater in rTOF compared to isolated pulmonary regurgitation (-26.5% versus -22.3%, p < 0.05). Longitudinal strain did not differ between groups. The longitudinal:circumferential strain ratio was significantly lower in rTOF compared to isolated pulmonary regurgitation (1.24 versus 1.53, p = 0.05). Circumferential and longitudinal strain rates did not differ between groups. CONCLUSIONS The right ventricles in rTOF demonstrate greater reliance on circumferential strain in response to increased volumes. The decrease in longitudinal:circumferential strain ratio suggests rTOF right ventricles display a greater adaptive response to the volume load than isolated pulmonary regurgitation, highlighting the importance of the relative contributions of both circumferential and longitudinal strain in order to understand the mechanisms of right ventricular dysfunction in pulmonary regurgitation.