Objective: The aim of our study was to study the course of the most common and potentially dangerous arrhythmia - atrial fibrillation (AF) in patients within 6 months after infection with COVID-19 (CI). Design and method: The study included 187 pts aged 62.5±0.9 years (47% men, 53% women). The first three groups formed 116 pts who had AF and underwent coronavirus infection (CI). The first group (G1) consisted of 36 patients who did not have AF before CI. The second group (G2) was represented by 25 patients in whom the transition of the paroxysmal form of AF into persistent, or persistent AF into its permanent form occurred. The third group (G3) consisted of 55 patients in whom the form of AF did not change. Results: Older age, female gender, hypertension, and coronary heart disease were clinical factors associated with the occurrence of AF or the worsening of the course of previously diagnosed AF in patients who underwent COVID-19. In addition, there were more pronounced signs of damage to the functional properties of the endothelium, the severity of systemic insufficient content in the blood of total cholesterol and TG, proatherogenic fractions of blood lipoproteins, which can be the cause of more clinically pronounced arrhythmias. Conclusions: A proportion of COVID-19 patients with newly diagnosed AF may have a pre-existing substrate for AF, and acute COVID-19 infection may be a trigger for the initiation of AF, consistent with a temporal relationship between new-onset AF and COVID-19 infection.