BACKGROUND: In this study, we aimed to evaluate the effects of electroconvulsive therapy (ECT) on cardiac autonomic functions (CAF) in patients with major depressive disorder (MDD) using heart rate variability (HRV) analysis. METHOD: Fourteen men joined the study. Nine ECTs were administered. Holter monitoring was performed before treatment and at the end of the first, third and sixth weeks of the treatment. The Hamilton Depression Rating Scale (HAM-D) was used to assess symptom severity. RESULTS: Seven patients responded to ECT. There was a change of 2-hour resting HF, pNN50 and RMSSD scores between week 0 and week 6. This change was not significant after week 1 and week 3. HRV values did not differ when we grouped the patients as responders and non-responders to ECT except the 2-hour resting HF value of responders between week 0 and week 6 and the 24-hour HF value of non-responders between week 1 and week 6. All observed changes showed a decrease in parameters. Overall, the LF/HF ratio did not change significantly in either analysis. HRV values did not correlate with HAM-D scores and no relation was found between treatment response and HRV analysis. After Benferroni-adjustment none of the changes were found statistically significant. LIMITATIONS: The limitations of the study are the small sample size and the absence of healthy controls. CONCLUSIONS: A consistent change in HRV was not observed in response to ECT in patients with MDD. Accepting the HRV as a promising surrogate marker of autonomic activity, ECT does not cause a significant change in nine male treatment resistant MDD patients cardiac autonomic functions.