The studies, performed with MRI and CT, showed that the increase of fat, immediately adjacent to the myocardium (epicardial fat) is correlated more strongly with the risk of atrial fibrillation than the general or abdominal obesity. According to some studies, epicardial fat around the left atrium is a strong predictor of the development at atrial fibrillation. Also, the amount of the fat is associated with the effectiveness of cardioversion and the risk of developing thromboembolic stroke in patients with atrial fibrillation. The number of such works is small, since tomographic examinations are not needed if intra-atrial thrombosis is suspected, and transthoracic echocardiograthy does not allow visualization of atrial fat. However, transesophageal echocardiography is widely used in patients with atrial fibrillation and allows to measure the structures that serve as depots of epicardial fat, namely the interatrial septum and left lateral ridge. Accumulation of epicardial fat leads to thickening of these structures. This can be used to study the relationship between epicardial obesity and the risk of thromboembolic complications in patients with atrial fibrillations.