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Background: Pulsed field ablation (PFA) is a novel nonthermal cardiac ablation technology based on irreversible electroporation (IRE). While areas of IRE lead to durable lesions, the surrounding regions, where reversible electroporation occurs, recover. The behavior of local electrograms in areas of different electroporation levels remains unknown. The goal of this study is to characterize electrogram dynamics after PFA in IRE and reversible electroporation areas., Methods: A total of 6 domestic swine were used. PFA was applied in the epicardium of the right and left ventricles using a focal monopolar catheter. Additional radiofrequency ablations were performed. Epicardial unipolar electrograms were acquired at baseline and for 60 minutes post PFA/radiofrequency ablation using a high-density electrode matrix attached to the epicardium. Electrogram dynamics were analyzed in areas corresponding to different levels of electroporation. Acute lesion formation was assessed after 3 to 5 hours by triphenyl tetrazolium chloride staining., Results: Electrogram analysis demonstrated a clear association between electrogram changes and the level of electroporation. Immediately after PFA, electrograms displayed the following: a significant decrease in R/S-wave amplitude; a large elevation of the ST-segment; and a large decrease in their |(dV/dt)| max . Marked changes in electrograms were observed beyond the lesion area. Thereafter, a gradual recovery was observed. The evolution of all the electrogram parameters throughout the 60 minutes after PFA was significantly different ( P <0.05) between the IRE and reversible electroporation areas. Acute lesion staining showed significantly larger depth for PFA lesions compared with radiofrequency ablation., Conclusions: This study shows that unipolar electrograms can differentiate between reversible electroporation and IRE areas during the first 30 minutes post ablation. Differences after the first 30 minutes are less evident. Our findings could result useful for immediate lesion assessment after PFA and warrant further investigation., Competing Interests: Disclosures Dr García-Sánchez is a consultant for Argá Medtech SA and Medlumics SL. Dr Guerra has served as consultant for Biosense Webster, Boston Scientific and Abbott, received speaker fees from Boston Scientific and Abbott, and received a research grant from Abbott and Medtronic. Dr Ivorra is a consultant for Argá Medtech SA and Medlumics SL. The other authors report no conflicts.