Quantitative information is needed on the directly depolarized area (DDA) induced by high-output energy during a precise mapping procedure to detect the origin of a tachycardia. In the present study, a DDA caused by high-output energy was quantitatively evaluated in the exposed canine heart. In 8 dogs, the right atrial and ventricular surfaces were exposed through a right thoracotomy and pacing with various outputs was delivered from the epicardial surface. A comb-shaped 16 polar electrode array and/or a 224 polar mat electrode array were used for recording the epicardial electrograms. The local activation time was measured at each electrode site, and the relationship of the distance between the electrode location from the pacing site and the local activation time was plotted and fitted to a primary regression line. The intercept of the regression line on the horizontal axis was defined as the radius of the ‘DDA’ and this was evaluated at each pacing output. The radius of the DDA was 0.6±0.1mm with a 2V and 3.8±0.2mm with a 10V output when it was evaluated in a direction perpendicular to the fiber orientation of the pectinate muscle, 0.8±0.1mm with a 2V and 4.1±0.3mm with a 10V output in a direction parallel to the pectinate muscle fiber orientation, and 0.9±0.3mm with a 2V and 3.6±0.5mm with a 10V output in the right ventricle. The DDA extended according to the increase in stimulation outputs at all sites, and there was no significant difference in the pacing site or the direction of the stimulation propagation. The DDA caused by high-output energy is a purely physical phenomenon that depends only on stimulation output and tissue resistance. The diameter of the DDA exceeded 4mm (ie, the size of a standard tip electrode for catheter ablation) when pacing was delivered with an output greater than 6V.