A 74-year-old woman with a VVI-rate-responsive pacemaker (Pacesetter 2033K; unipolar pacing electrode) was admitted for cardioversion of atrial tachycardia. Antiarrhythmic medication included flecainide 100 mg x 2. Electrical defibrillation was followed by transient, but severe nodal bradycardia and pacemaker malfunction characterized by loss of ventricular capture and sensing. The incident probably represents an example of pacemaker failure due to an acute increase in the stimulation threshold, most likely caused by current-induced tissue damage at the electrode-endomyocardial interface. Flecainide might have contributed to the increase in stimulation threshold. The clinician should be prepared for the possible consequences of pacemaker failure after external defibrillation.