The aim of the research was to evaluate safety and elaborate criterions for early cardioversion (without 4 weeks of warfarin treatment) in patients with long-term atrial fibrillation (AF), guided by transesophageal echocardiography (TEE). We examined 131 persistent AF patients: mean age 58.67±0.85 years and mean term of the AF paroxysm 5.08±1.35 days; 87 % patients were with coronary artery disease; 2.29 % – with metabolic cardiomyopathy, 9.16 % – with myocardiofibrosis and 0.76 % – with hypertrophic cardiomyopathy. 84 % patients had arterial hypertension. In 43.5 % patients the current paroxysm was first. We divided all patients in two groups: 1st – those who were cardioverted immediately after TEE, and 2nd – those in whom cardioversion was postponed for at least 4 weeks. There were no thromboembolic events in 10 days following cardioversion in both groups. Regression models for thrombus prediction by transthoracic echocardiography appear to be weak because of low sensitivity (14.3 %), so TEE should be performed for all patients for its exclusion. We showed that in patients with long term AF TEE guided approach can safely reduce the term before cardioversion in 60.3 %. We also showed that in a case of effective anticoagulation we could perform cardioversion even in patients with moderate and dense spontaneous echo-contrast. There are no signs evaluated by means of transthoracic echocardiography that could predict left atrial appendage thrombi.