The aim of the research was to study peculiarities of origin, course and mutual effects of atrial fibrillation and heart failure. 983 patients were observed. It was detected that mean and minimum heart rate registered by Holter ECG monitoring increased according to the stage of heart failure in patients with atrial fibrillation. The number of single, bigeminal ventricular ectopic beats, ventricular ectopic beats index per 1000 beats, the number of the episodes of ventricular tachycardia as well as the indices of supraventricular ectopic beats, supraventricular tachycardia, the index of supraventricular beats per 100 increased depending on stage of
heart failure. The signs of myocardial ischemia significantly increased as well. We also detected decrease of effective and functional atrial refractory periods, the impairment of atrial functional properties.