Inappropriate therapy from implantable anti-tachyarrhythmia devices is a common problem with a variety of etiologies. The verification of arrhythmias or other sensed events that precipitate defibrillating shocks is difficult with first- and second-generation devices due to the absence of sufficient data storage and the inability to examine stored and real-time intracardiac electrograms. In addition, the absence of premonitory symptoms is an unreliable marker for the appropriateness of defibrillator shocks. The incorporation of improved data storage and the ability to inspect intracardiac electrograms in newer devices have greatly increased the ability to diagnose abnormal device behavior as shown in the following case report. Inappropriate implantable cardioverter defibrillator discharge due to myopotential sensing is described. The diagnosis was facilitated by telemetered intracardiac electrograms.