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Background: Spatial heterogeneity in repolarization plays an important role in generating and sustaining cardiac arrhythmias. Reliable determination of repolarization times remains challenging., Objectives: The goal of this study was to improve processing of densely sampled noncontact unipolar electrograms to yield reliable high-resolution activation and repolarization maps., Methods: Endocardial noncontact unipolar electrograms were both simulated and recorded in pig left ventricle. Electrical activity on the endocardial surface was processed in terms of a pseudo-electric field. Activation and repolarization times were calculated by using an amplitude-weighted average on QRS and T waves (ie, the E-field method). This was compared vs the conventional Wyatt method on unipolar electrograms. Timing maps were validated against timing on endocardial action potentials in a simulation study. In vivo, activation and repolarization times determined by using this alternative E-field method were validated against simultaneously recorded endocardial monophasic action potentials (MAPs)., Results: Simulation showed that the E-field method provides viable measurements of local endocardial action potential activation and repolarization times. In vivo, correlation of E-field activation times with MAP activation times (r E  = 0.76; P < 0.001) was similar to those of Wyatt (r Wyatt  = 0.80, P < 0.001; P[h 1 :r E > r Wyatt ] = 0.82); for repolarization times, correlation improved significantly (r E  = 0.96, P < 0.001; r Wyatt  = 0.82, P < 0.001; P[h 1 :r E > r Wyatt ] < 0.00001). This resulted in improved correlations of activation-repolarization intervals to endocardial action potential duration on MAP (r E  = 0.96, P < 0.001; r Wyatt  = 0.86, P < 0.001; P[h 1 :r E > r Wyatt ] < 0.00001). Spatial beat-to-beat variation of repolarization could only be calculated by using the E-field methodology and correlated well with the MAP beat-to-beat variation of repolarization (r E  = 0.76; P = 0.001)., Conclusions: The E-field method substantially enhances information from endocardial noncontact electrogram data, allowing for dense maps of activation and repolarization times and derived parameters., Competing Interests: Funding Support and Author Disclosures The work was supported by grants from KU Leuven BOF, C14/18/079, to Drs Willems and Claus and from Fund for Scientific Research-Flanders (FWO) G097021N to Drs Claus and Sipido. Dr Willems is supported as Senior Clinical Investigator and Dr Amoni as PhD fellow by the Fund for Scientific Research-Flanders (FWO)., (Copyright © 2023 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)