Introduction: Late complications after tetralogy of Fallot repair (rTOF) often arise from chronic pulmonary regurgitation (PR). Prospective studies of outcomes in those with rTOF and significant PR are lacking.Hypothesis: We hypothesized that cardiovascular magnetic resonance imaging (CMR) imaging measurements would be associated with poor outcomes in an “at risk” population with rTOF and ≥moderate PR.Methods: This was a prospective, international study (North America, Europe and Asia) of children and adults. Inclusion criteria were rTOF in childhood, age ≥12 years, ≥moderate PR, and CMR within 18 months of enrollment. All CMR analysis occurred in a central core laboratory. Patient reported outcomes were collected using standardized tools. The primary clinical outcome was death or sustained (>30 seconds) ventricular tachycardia (VT) recorded at 3 year follow-up.Results: We enrolled 629 patients (55% male) at 29±14 years (2013-2017). Primary rTOF was done at 1.6 years (IQR 0.6,4.2) with a transannular patch in 55%. By standardized symptom assessment, 78% were asymptomatic (NYHA 1). Baseline CMR findings included PR fraction 38±14%, right ventricular (RV) end-diastolic volume indexed (EDVi) 155±41mL/m2, RV ejection fraction (EF) 44±7%, RV mass indexed 59±16 g/m2, left ventricular (LV) EDVi 85±18mL/m2, LVEF 55±7% and LV mass indexed 88±27 g/m2. Outcomes at 3 years were recorded (available in n=101). During follow-up, surgical pulmonary valve replacement (PVR) occurred in 38 patients (38%). In the PVR group compared with the non-PVR group, baseline RVEDVi was larger (189 vs. 152 mL/m2, p<0.0001) and RV mass was higher (65 vs. 58 g/m2, p=0.04); RVEF, LVEF and LV mass did not differ between groups. At 3 year follow-up, 4 patients (4%) had an outcome (n=2 deaths, n=2 VT) and half of these patients (n=2) had PVR. Those with outcomes had higher baseline RV mass and LV mass as compared to those without outcomes (73±12 vs. 59±13g/m2, p=0.04 and 132±32 vs. 89±28g/m2, p=0.01); volumes and function did not differ between groups.Conclusions: Despite significant PR, most patients with rTOF were asymptomatic. At 3 year follow-up, PVR occurred in more than one third of patients. Death or VT was observed in a small number of patients who had higher RV and LV mass on baseline CMR.