Atrial fibrillation is the most common arrhythmia, in emergency rooms and around the globe.Its frequency is constantly increasing and the likelihood of a physician encountering it at any time is high.Usual treatment approaches are "conservative," traditionally including heart rate control, anticoagulation and hospitalization.The main goal with this approach is stroke prevention.As time goes by, atrial remodeling takes place and the chance to restore sinus rhythm decreases.A longer time in atrial fibrillation leads to more structural heart disease.Thus, adequate management in the emergency room for an initial or complicated episode reduces the risk of inadequate therapies and healthcare costs.This review will focus on the approach to atrial fibrillation in the emergency room according to current evidence.