Atrial fibrillation (AF) is the most common chronic arrhythmia and is characterized by erratic atrial electrical activity with atrial rates of 400-600 beats per minute.AF in regards to symptoms and thromboembolic risk (including stroke).The symptoms of AF are related to the loss of atrial mechanical activity (atrial contraction) and rapid ventricular heart rates both of which can reduce cardiac output and lead to congestive heart failure. Thromboembolism frequently cause stroke in AF patients.It’s happened in Mongolia more than in other countries. That is why there is big need to improve knowledge of familiar, local, district and other professional doctors. The lecture was written using guidelines for the management of atrial fibrillation.