Atrial fibrillation (AF) is a supraventricular tachyarrhythmia characterized by chaotic electrical activity of theatria (350–700 beats per minute) and absolute irregularity of the heart beats on electrocardiography (ECG).The prevalence of AF is 1–2% of the general population. It should be noted that this rate is increasing everyyear. Researchers pay much attention to the study of the functional characteristics of the left atrium in case ofAF, considering its important functions: on the one hand, it is a reservoir, receiving blood from the pulmonaryveins during of ventricular systole and acts as a conduit during the phase of early diastolic filling of the leftventricle, directing the blood flow to the left ventricle; on the other hand, the left atrium performs a pumpingfunction, providing 15–30% of the left ventricle stroke volume due to active depletion at the end of the diastole of the ventricles. Changes of the basic functions of the left atrium in AF are caused by the following histo-logical changes of myofibrils: hypertrophy, degeneration, myolysis and fibrosis. Contrast-enhanced computedtomography (CT) and magnetic resonance imaging (MRI) allows to precisely assess the functional and morphological characteristics of the left atrium in AF, which are extremely important for prediction the risk ofcomplications of AF, determination of the treatment modality in these patients and prediction of the successrate of AF surgical treatment. The functional characteristics of left atrium include the ejection fraction of theleft atrium, morphological – its volume, the size of the orifice, the anatomy of the pulmonary veins and leftatrium appendage, and, finally, fibrosis of the myocardium of the left atrium. Anatomy of the left atrium andpulmonary veins is considered to be an important factor while planning interventional treatment of AF (RFisolation of pulmonary veins). CT and MRI allow to reveal thrombosis of the left atrium appendage thatenables us to start anticoagulation therapy, to select the appropriate type and size of the device for percutaneous closure of the left atrium appendage and to plan its ligation during open heart surgery for the prevention of ischemic stroke in these patients. Today contrast-enhanced CT and MRI allow non-invasively assess with high accuracy functional and morphological characteristics of the left atrium in patients with AF. High diagnostic value of CT and MRI is confirmed by the fact that the linear dimensions of the left atrium and pulmonary veins coinciding with those ofinvasive methods (intracardiac echocardiography and venography), and fibrosis of the left atrium is confirmed by the results of histological examination.