INTRODUCTION Restoring sinus rhythm in patients with atrial fibrillation (AF)/atrial flutter (AFl) requires adequate oral anticoagulation prior to direct current cardioversion (DCC). Some patients eligible for DCC are not properly anticoagulated. OBJECTIVES The aim of the study was to assess risk factors for thrombus and spontaneous echo contrast (SEC) in the left atrium (LA) as well as the safety profile of transesophageal echocardiography (TEE)-guided DCC in patients with inadequate anticoagulation. PATIENTS AND METHODS From the cohort of 316 patients admitted for DCC, 139 patients (mean [SD] age, 63.4 [11.5] years) had inadequate anticoagulation; 91 patients were admitted urgently for acute coronary syndrome, heart failure (HF), or poor tolerance of arrhythmia. The mean (SD) CHA2DS2‑VASc score was 3.0 (1.7). RESULTS TEE revealed a left atrial appendage (LAA) thrombus in 16 patients (11.5%), and SEC in the LA in 63 patients (45.3%). In a univariate analysis, LAA thrombus was more common in patients after myocardial infarction (odds ratio [OR], 3.92; 95% CI, 1.34-11.48; P = 0.009), while SEC in the LA was more common in patients with HF (OR, 2.23; 95% CI, 1.1-4.53; P = 0.02) and left ventricular ejection fraction of less than 40% (OR, 3.65; 95% CI, 1.66-8.06; P = 0.001). In a multivariate model, the most powerful SEC‑predicting factor was the LA size exceeding 45 mm (OR, 3.08; 95% CI, 1.3-7.29). DCC was performed in 105 patients. No complications of TEE or DCC were observed. CONCLUSIONS AF/AFl inadequately treated with oral anticoagulation predisposes to thrombus formation and SEC in the LA. Once thrombus is excluded, DCC is a safe procedure. There were no predictors of LAA thrombus; therefore, TEE before DCC should be performed in all patients with AF/AFl in accordance with the guidelines.