A 79-year-old woman without structural heart disease underwent catheter ablation of ventricular tachycardia. Successful ablation was achieved on the left ventricular epicardium using an epicardial approach via pericardial puncture. Thereafter, programmed stimulation induced ventricular fibrillation (VF). A 360 J biphasic extrathoracic cardioversion using cutaneous pads in the conventional sternal-apical position failed to terminate the VF. After repositioning the sternal pad more laterally, the 360 J biphasic shock terminated the VF. Fluoroscopic imaging revealed aspirated air in the pericardial space, mainly apically. In this case, air aspirated into the pericardial space during the epicardial approach might have elevated the defibrillation threshold. © 2008 Elsevier Ltd. All rights reserved.