OBJECTIVE: Low heart rate variability (HRV) has been confirmed in heroin users, but the effects of heart-rate-variability-biofeedback in heroin users remain unknown. This study examined (1) correlations between depression and HRV indices; (2) group differences in HRV indices among a heroin-user group, a group with major depressive disorder but no heroin use, and healthy controls; and (3) the effects of heart-rate-variability-biofeedback on depressive symptoms, HRV indices, and respiratory rates within the heroin group. METHODS: All participants completed a depression questionnaire and underwent electrocardiogram measurements, and group differences in baseline HRV indices were examined. The heroin group underwent electrocardiogram and respiration rate measurements at baseline, during a depressive condition, and during a happiness condition, before and after which they took part in the heart-rate-variability-biofeedback program. The effects of heart-rate-variability-biofeedback on depressive symptoms, HRV indices, and respiration rates were examined. RESULTS: There was a negative correlation between depression and high frequency of HRV, and a positive correlation between depression and low frequency to high frequency ratio of HRV. The heroin group had a lower overall and high frequency of HRV, and a higher low frequency/high frequency ratio than healthy controls. The heart-rate-variability-biofeedback intervention increased HRV indices and decreased respiratory rates from pre-intervention to post-intervention. CONCLUSION: Reduced parasympathetic and increased sympathetic activations were found in heroin users. Heart-rate-variability- biofeedback was an effective non-pharmacological intervention to restore autonomic balance.