Atrial fibrillation (AF) is an arrhythmia frequently seen in the postoperative period of cardiac surgery. In this context, it is associated with the presence of comorbidities, longer length of hospital stay, and higher costs related to surgery. The mechanisms involved in the genesis of AF in the postoperative period of cardiac surgery (AFPO) are different from those causing paroxysmal AF. Knowledge of these mechanisms permits the use of efficient measures to reduce the incidence of this arrhythmia. According to recommendations of the literature, treatment is efficient and safe, because the rates of reversion to sinus rhythm are high and complications are reduced, and it is not associated with a high frequency of side effects.