Atrial fibrillation is the most common complications after cardiac surgery, occurring in 20-60% of patients depending on definition and diagnostic methods. Usually appears between 2 and 4 day after operation and often turns back during first 30 days in postoperative time. Treatment of this complication is often protracted, requiring increased monitoring and hospital resources, and extending hospital length of stay Clinical consequences can be significant and include hemodynamic instability and stroke. Recently we can see the increase of atrial fibrillation's frequency occurrence. It is related both with enlargement of patients qualified to cardiac operations and with more and more severe conditions of patients subjected to surgery. Despite of existence unique guidelines there are still many doubts, regarding to choice of antiarrhythmic agent, optimal time of therapy initiation or performing invasive treatment. Atrial fibrillation influences the worsening of patient's postoperative condition (e.g. significantly increasing postoperative mortality) and considerably increases the costs of hospitalization. Therefore competent prevention and suitable treatment of postoperative atrial fibrillation is one of the most important tasks for cardiac surgeons or clinicians who manage the patients after cardiosurgical operations.