Aim. To determine heart rate variability (HRV) in depressed patients with chronic coronary artery disease (CAD) and to assess the effects of agomelatine on HRV.Methods. 74 patients with CAD (class 3-4 angina pectoris) were recruited in a study. Patients (n = 45) with CAD and depression were assigned to Group 1, whereas CAD patients (n = 29) without any signs of depression were assigned to Group 2. 17 patients received agomelatine (Subgroup 1) and 28 patients did not take any antidepressants (Subgroup 2). HRV was measured using SCHILLER MT-200 Holter-ECG apparatus at baseline and after 6 months.Results. Patients with depression demonstrated a significant decrease in HRV compared to non-depressed patients (pNN50% (3.9 [2.2; 5.4] vs 5.7 [2.9; 12.6], p = 0.03), SDANN (81 [63; 97] ms vs 91 [79; 102] ms, p = 0.06), SDNNindx (46 [36; 56] ms vs 55 [48; 66] ms, p = 0.002), rMSSD (28 [21; 36] ms vs 33 [ 29; 45] ms, p = 0.02), SDNN (97 [75; 121] ms vs 110 [98; 127] ms, p = 0.02). Subgroups 1 and 2 did not differ in HRV (p>0.05). After 6 months, significant differences in the following parameters were found in those patients who received agomelatine therapy and those who did not: rMSSD (36.5 [28.5; 51] ms vs 26.5 [25; 32] ms, p = 0.02), SDANN (88 [72,5; 114,5] ms vs 67,5 [58; 83] ms, p = 0.03), SDNN strives to a significant difference - 100 [87; 133.5] ms vs 85.5 [75; 103] ms, p = 0.07.Conclusion. HRV significantly decreased in depressed patients with CAD suggesting autonomic dysfunction and worsening their prognosis. Agomelatine therapy in patients with CAD is effective in treating heart rate variability and reducing the risk of developing life-threatening arrhythmias.Key