Background: A large Dispersion of Repolarization (DoR) is associated with an increased arrhythmogenic risk. This can be measured clinically by calculating the Activation Recovery Interval (ARI) to estimate Action Potential Duration (APD). However, the ability of ARI to accurately predict APD dispersion in patients with repolarization abnormality has not been determined. Objective: Compare DoR computed from ARI in patients with optical mapping of human hearts to establish whether ARI accurately measures DoR in repolarization abnormalities. Methods: Optical mapping (OM) was performed on the left ventricles of 4 explanted human hearts (septal hypertrophy, concentric hypertrophy, 2 healthy). APD and repolarization times were measured endo- and epicardially on the anterior of the LV. Electroanatomic mapping was performed with CARTO over the entire endo- and epicardial surfaces of 3 patients with idiopathic VF or Brugada syndrome. An average of 271 points were recorded on the RV endocardium, 250 on the LV endocardium and 2514 epicardially. Activation and ARI were calculated. DoR, based on OM or ARI, was calculated by use of Moran’s I, with a value of 1 signifying perfect spatial correlation. Results: APD and ARI were consistent between mapping methods. For OM, the DoR averaged over the four hearts was 0.81 overall, and was 0.90 and 0.73 for epi- and endocardium, respectively. From ARI, the overall average DoR was 0.90, with values of 0.90 and 0.90 for epi- and endocardium, respectively. Conclusion: APD distribution, and consequently DoR, agree between mapping methods. Measuring DoR by ARI accurately assesses the underlying repolarization abnormalities in patients.