Programmed upper rate pacing occurred in a patient with a rate-adaptive pacemaker when he was connected to a cardiac monitor in an emergency department. The tachycardia was mistakenly interpreted to be ventricular tachycardia and the patient received multiple DC shocks as well as intravenous amiodarone and sotalol, resulting in severe hemodynamic deterioration. It is important that physicians working in the hospital environment be familiar with this pacemaker-monitor interaction as the problem may be easily rectified by disconnecting the monitor or by reprogramming the pacemaker to a nonrate-adaptive pacing mode.