BACKGROUND: Postictal suppression on an electroencephalogram (EEG) represents electrical silence during electroconvulsive therapy (ECT) and has been considered as a key feature associated with the efficacy of treatment. The present study aimed to predict postictal suppression using heart rate variability (HRV). METHODS: Participants comprised 21 consecutive patients with depression who underwent bilateral pulse wave ECT. We analyzed the frequency domains of resting HRV before ECT. HRV indices such as the high-frequency component (HF) reflecting parasympathetic activity and the ratio of low-frequency component (LF)/HF reflecting sympathetic activity were natural log transformed for analysis. We evaluated ictal and peri-ictal EEG parameters and investigated their associations with HRV indices. RESULTS: Postictal suppression and regularity were positively associated with ln[HF]. Postictal suppression remained significantly associated with ln[HF] after adjusting for age in multiple regression analysis of patients with depression. LIMITATIONS: The present study could not examine the influence of diabetes mellitus, hypertension and polarity on HRV. In addition, the small sample size resulted in low statistical power. CONCLUSIONS: These results suggested that ln[HF] before ECT could be utilized as a predictor of postictal suppression on EEG during ECT.