This case describes "double counting" of intrinsic conduction due to the combination of intraventricular conduction delay and the merging of the electrograms from the right and left ventricle (coronary sinus) leads in a biventricular cardioverter defibrillator. This situation prompted asymptomatic antitachycardia pacing. Lengthening of AV conduction by betablocker solved the problem.