Introduction: Ventricular tachyarrhythmia circuits are occasionally found to be epicardial. Several anatomical obstacles could prevent successful ablation from epicardial approach. One of them would be fatty tissue covering ablation targets. Epicardial fat can mimic scar tissue during mapping and reduce ablation efficiency due to shielding effect. This study was designed to search for differential parameters in ventricular electrograms between epicardial fat areas versus ventricular myocardium. Methods: Five anesthetized open-chest dogs were evaluated. Ventricular electrograms during sinus rhythm were obtained epicardially using a 2-mm tip electrode catheter from epicardial fat areas of the left ventricle (FAT, n = 5) and the right and left ventricular myocardium (NONFAT, n = 10). Amplitude and power spectrum were analyzed in each site. High frequency (HF) area was defined as an area of frequency > 70 Hz in power spectrum curve of each electrogram. Results: FAT showed tendency of lower amplitude and higher HF component than NONFAT, but there were no statistically significant differences in electrogram amplitude (4.9짹3.2 vs. 5.7짹3.0 mV, p = 0.513) and ratio of HF area (HF area / total area of power spectrum curve: 0.46짹0.27 vs. 0.32짹0.15, p = 0.513) between FAT versus NONFAT. Ratio of HF area > 0.62 had 100% specificity and 40% sensitivity in epicardial fat detection. Conclusion: Characteristics of ventricular electrogram might be altered by epicardial fat. Large range of values in amplitude and spectrum pattern was overlapped each other between FAT and NONFAT. However electrograms with big HF component may indicate epicardial fat.