Heart failure (HF) is a debilitating and fatal condition characterised by sympathetic activation and parasympathetic withdrawal. Tackling the underlying autonomic imbalance through parasympathetic stimulation can improve cardiac function and quality of life scores in HF patients1, however, the current method of cervical vagus nerve stimulation (VNS) is invasive and associated with side effects. This study investigated the autonomic effects of a non-invasive method of VNS – transcutaneous electrical stimulation of the auricular branch of the vagus nerve (tVNS) – in healthy participants (n = 111; 58 female, 53 male; aged 20-66 years) and HF patients (n = 6; 1 female, 5 male; 51-86 years). The study was approved by the University of Leeds Ethics Committee and the National Research Ethics Service and was conducted in accordance with the Declaration of Helsinki. Heart rate (ECG), blood pressure and respiration were recorded continuously. Heart rate variability (HRV) was calculated using spectral analysis of beat-to-beat intervals derived from ECG data. Low frequency (LF; 0.04-0.15Hz) and high frequency (HF; 0.15-0.40Hz) power were calculated. HF power represents parasympathetic/vagal modulation of heart rate and the ratio of low to high frequency power (LF/HF) can be used as an indicator of sympathovagal balance, such that a decrease in LF/HF indicates a shift in autonomic balance towards parasympathetic dominance. Microneurography was also used to record muscle sympathetic nerve activity (MSNA; n = 10). tVNS was applied at either low pulse width and pulse frequency (L-tVNS), high pulse width and pulse frequency (H-tVNS) or sham stimulation. Data were analysed at baseline, during tVNS and during recovery. Repeated measures ANOVAs were used to analyse results (data presented as mean ± S.E.M). L-tVNS (n = 63) and sham tVNS (n = 14) had no significant effect on HRV whereas HRV improved significantly during H-tVNS in healthy participants with a decrease in LF/HF ratio from 1.26 ± 0.15 at baseline to 1.04 ± 0.14 during H-tVNS (n = 34; p = 0.026). There was a significant reduction in single unit MSNA frequency and incidence during H-tVNS (p = 0.001 and p = 0.002 respectively). H-tVNS significantly improved LF/HF ratio in HF patients from 4.78 ± 1.49 to 3.13 ± 1.39 (n = 6; p = 0.028). There was also a significant reduction in LF power during H-tVNS in HF patients (p = 0.028). Based on the results of this study, tVNS can improve HRV in both healthy participants and HF patients. Furthermore, microneurography revealed that the improvement in HRV during H-tVNS is, at least partly, due to a reduction in sympathetic activity in healthy participants. tVNS could be a practical, non-invasive and economical therapy for heart failure patients and warrants further investigation.