Coil embolization is a safe therapy for pulmonary arterio-venous malformations (PAVMs). We report the case of a 72-year-old woman affected by hereditary hemorrhagic teleangectasia who experienced right bundle branch block and atrial fibrillation 36 hours after embolization of an extended PAVM. To our knowledge, this is the first case of such a complication of embolization of a pulmonary fistula, presumably due to an acute pressure overload on both the right atrium and ventricle. This case report suggests that, after embolization of extended pulmonary fistulas, patients should be carefully monitored for rhythm disturbance and new onset of intraventricular conduction defects.