This study examines the relationship the extracellular volume fraction (ECV) measured using cardiac magnetic resonance (CMR) T1 mapping and cardiac events in symptomatic adults with tetralogy of Fallot (the most common form of cyanotic congenital heart disease). A correlation is found between right ventricular (RV) volume and ejection fraction (EF); with RV- and septum-extracellular volumes (ECV) in this disease. In particular, the combination of septum-ECV and RVEF was a useful predictor, compared to the use of a single CMR parameter. This study supports SDG 3 Good health and wellbeing.