Knowledge of the anatomy of the left atrium plays an important role not only in the surgical treatment of atrial fibrillation, but also from the standpoint of understanding the fundamentals of the pathogenesis of atrial fibrillation. The main components of the left atrium are the venous part, atrial vestibule, body and appendage. Atrial myocardium traction surrounding pulmonary vein orifices serves as a trigger that initiates atrial fibrillation. The structural and spatial organization of muscle fibers of ‘sleeves’ of the left atrium and pulmonary veins explains such arrhythmogenic properties of this area. The ablation of pulmonary vein orifices is conducted in the treatment of the paroxysmal form of atrial fibrillation. Knowledge of topographic and anatomic relations between the left atrium and surrounding structures allows to avoid such complications as atrioesophageal and coronary-cardiac fistulas, injury of the phrenic, vagus and left recurrent nerves. Particular attention should be paid to the left atrial appendage due to the most frequent localization of clots in it and due to the risk of thromboembolic complications associated with atrial fibrillation. Atrial fibrillation causes significant changes in the left atrium that involve anatomical and electrophysiological remodeling. The volume of the left atrium in case of atrial fibrillation increases significantly exceeding several times the normal values. Knowledge of the anatomy of the left atrium and the use of modern methods of examination allow to obtain detailed information on the left atrium condition and to plan the intraoperative phase more accurately.