Atrial fibrillation is one of the most common arrhythmias in the world, which can occur as a complication in up to 27 % of cases in patients with acute myocardial infarction. The article presents the results of a study in which 114 patients with acute myocardial infarction took part. Follow-up was carried out for 1 year after myocardial infarction. All patients were divided into 4 groups according to gender and the presence of atrial fibrillation. According to the data of 24-hour ECG monitoring, the indicators of rhythm and conduction disturbances were assessed. When comparing groups of men and women with atrial fibrillation and sinus rhythm, it was found that statistically significant differences in same-sex groups with atrial fibrillation and sinus rhythm were: the duration of the PQ interval in the daytime and at night, the number of single, paired and group supraventricular extrasystoles. Thus, pathological supraventricular ectopic activity, in the form of extrasystolic arrhythmia, had a direct relationship with the development of atrial fibrillation, and impaired AV conduction (in the form of a prolongation of the PQ interval on the ECG) had an inverse relationship.