The aim of the study was to determine whether transthoracic echocardiography may predict severe left atrial appendage (LAA) dysfunction (low left atrial appendage velocity, severe spontaneous echo contrast, left atrial appendage thrombus) in patients with non-valvular atrial fibrillation (AF). Consecutive 588 patients underwent transesophageal echocardiography for assessing left atrial appendage function before cardioversion. Mean age was 59.03 years, mean CHA2DS2VASc score – 1.82 and mean LAA velocity – 36.06 cm/s. Severe spontaneous echo contrast was defined in 5.77 of cases, LAA velocity ≤ 25 cm/s – in 23.77 and LAA thrombus – in 5.57. Echo signs of left ventricular systolic and diastolic dysfunction and left atrial dilatation were found to be most significantly related to the severe LAA dysfunction. In conclusion, transthoracic echocardiography is a useful tool for evaluation of risk of severe LAA dysfunction in patients with non-valvular AF.