The aim: to analyze and find the connections between Holter ECG monitoring indexes and gut microbiota composition in patients with coronary artery disease and atrial fibrillation. Materials and methods. 300 patients were divided into 3 groups: first (CAD) — 149 patients with CAD but without arrhythmias, second (CAD+AF) — 124 patients with CAD and AF paroxysm, and the control group — 27 patients without CAD and arrhythmias. Results. The II group patients are characterized by an increase in Pseudomonadota (by taxonomic analysis), Actinobacter spp. and a decrease in Blautia spp., Bacteroides thetaiotaomicron in comparison with the I group, p<0.05. Total supraventricular extrasystoles are significantly correlated with Verrucomicrobiota (Akkermansia muciniphila, r=–0.340), p<0.05. Total VE is significantly correlated with Pseudomonadota (r=0.356), F/B ratio (r=–0.468) — by phylum analysis, and by specises analysis — Blautia spp. (r=–0.336), Actinobacter spp. (r=0.325), Eubacterium rectale (r=–0.327), and Roseburia inulinivorans (r=–0.317), p<0.05. The AF paroxysm occurrence is significantly correlated with Actinobacter spp. (r=0.309) and Eubacterium rectale (r=–0.328), p<0.05. ST-segment changes are correlated only with Streptococcus spp. (r=0.369), p<0.05. Conclusion. Gut microbiota species (Akkermansia muciniphila, Blautia spp., Actinobacter spp., Eubacterium rectale, Roseburia inulinivorans, Streptococcus spp.) are significantly correlated with rhythm abnormalities (supraventricular and ventricular) and ST-segment changes.