Background: Patients with atrial fibrillation (AF), lasting >48 h, considered for cardioversion, are recommended ≥3 weeks of oral anticoagulation before sinus rhythm restoration because of high risk of development of left atrial thrombosis (LAT) and stroke. However, the optimal duration of anticoagulation in the presence of overt LAT is unknown. Methods: An open-label study, aiming to investigate the prevalence of spontaneous echo con-trast (SEC) and LAT before and after 3 weeks of direct oral anticoagulant (DOAC) treatment. We included 51 consecutive patients (50.9% males), mean age 69.3±7.4 years with paroxys-mal/unknown duration of AF, considered for cardioversion, who agreed to have transesophage-al echocardiography at enrollment and 3 weeks later. Results: At baseline SEC was present in 26 (50.9%) and LAT in 10 (19.6%) of 51 patients. After 3 weeks on DOAC, SEC persisted in 12 (25.0%) and LAT in 7 (14.5%) of 48 patients, p<0.05 vs base-line. Factors, associated most strongly with persistence of SEC/LAT were left atrial appendage (LAA) emptying velocity <20 cm/s (OR=2.82), LAA lobes >2 (OR=1.84) and indexed left atrial volume ≥34 ml/m2 (OR=1.37). Conclusions: The recommended minimal period of 3 weeks of oral anticoagulation lead to SEC/LAT resolution in 47% of our patients. To our opinion, LA/LAA morphology and function should be taken into account when determining the duration of DOAC treatment before planned cardioversion.