The review evaluates the contribution of transoesophageal echocardiography as to the improvement of management of patients with atrial fibrillation. It emphasises the severity of fibrillation arrhythmia regarding the haemodynamic complications, but especially those arising from embolism causing significant morbidity and mortality, especially in the aged patients with organic heart diseases. An essential improvement in the imaging of the left atrium, but especially of its auricle has enabled a significant progress in the conception of the origin of thromboembolic complications after cardioversion of atrial fibrillation. The detection of thrombi in the left atrial auricle which had until now been impossible, enabled to postpone the patients, by use of transoesophageal echocardiography, for the considered cardioversion, thus reducing the risk of thromboembolism. On the other hand, the transoesophageal examination of the left atrial auricle by use of two-dimensional and doppler echocardiographies has enabled to judge the function of the left atrial auricle not only from the anatomical aspect, but also from that of pathophysiology. This fact enabled to stratify the patients at higher risk of thromboembolism, or vice versa, to select patients appropriate for the planned cardioversion of fibrillation arrhythmia, even if this state has been relatively prolonged. The current knowledge and experience are encouraging and it can be anticipated that within the course of a short period, the transoesophageal echocardiography will play an important role in the management of patients with atrial fibrillation. (Tab. 1, Fig. 3, Ref. 40)