We report on a 70 year old man with symptomatic atrioventricular node re-entry tachycardia and status post pacemaker implantation who underwent an electrophysiologic study for modulation of the slow pathway. The following night, the ICU monitoring alarm system indicated ventricular fibrillation (A). However, the patient was adequately responsive after wakening, and showed no symptoms of dizziness. During the next hours, three similar episodes occurred. Spectral analysis of the signal showed a peak at 5.5 Hz (B). The patient was known to have Parkinson’s disease for seven years. A resting tremor known to be in the range between 4 to 6 Hz is the most likely cause for these events. The muscular potentials are superposed on pacemaker signals and myocardial potentials, respectively (C).