Electrophysiologic studies had been performed before and after pharmacologic autonomic blockade (propranolol 0.2 mg/kg and atropine 0.04 mg/kg body weight) in a 23-year-old female patient with documented sinus arrest of 27 sec duration. Normal electrophysiologic findings before and after autonomic blockade excluded intrinsic sinus node dysfunction. Sinus arrest is therefore though to be due to an intermittent dysregulation of the autonomic nervous system.