Introduction: The limited success of ventricular arrhythmia ablation may be related to incomplete understanding of endocardial and epicardial dissociation, especially in diseased human hearts. Comparing healthy and pathological tissues can reveal how transmural electrical differences contribute to arrhythmogenesis and guide ablation strategies. Methods: We used a panoramic dual optical mapping system to simultaneously record transmembrane voltage from the endocardium and epicardium of three porcine (healthy) and two human (diseased) hearts. Hearts were perfused in a modified wedge preparation, allowing direct access to both surfaces. Red LEDs (660 nm) and the voltage-sensitive dye JPW-6003 enabled optical recordings at 500 Hz using two high-speed cameras. Signals were processed with spatiotemporal filtering, and local activation time (LAT) and action potential duration at 80% repolarization (APD80) were extracted. Restitution curves were constructed for each pacing cycle length (PCL), decreased from 1000 ms until conduction block or arrhythmia. Results: At PCL = 800 ms, porcine hearts showed similar APD80 values between surfaces (endo: 302.0 ms, SD = 39.6; epi: 297.2 ms, SD = 46.0). Human hearts exhibited longer and more heterogeneous repolarization (endo: 469.5 ms, SD = 93.2; epi: 429.4 ms, SD = 76.7). In pigs, fibrillation occurred near PCL = 240 ms without alternans. In contrast, human hearts showed early and pronounced APD alternans starting at PCL = 230 ms, especially in the endocardium, where APD80 reached 600 ms. LAT maps during fibrillation revealed conduction block and reentrant sites in the human endocardium, while the epicardium showed slower and disorganized propagation. Conclusion: The study revealed distinct electrophysiological behaviors between healthy porcine and diseased human hearts. While porcine hearts provided a physiological baseline, human hearts showed marked APD alternans and discordant restitution. These findings highlight the importance of capturing transmural dynamics and reinforce the translational value of this approach for understanding arrhythmia mechanisms.