Heart failure is a prevalent health concern within the western world. It has huge economic, financial and personal implications. Despite the development of several clinically available treatments, heart failure associated mortality remains high. Heart failure patients display with dysfunction of the autonomic nervous system, including a high degree of vagal withdrawal. Consequently, the up-regulation of cardiac vagal tone, using vagal nerve stimulation (VNS) has recently gained attention as a potential new therapeutic approach to the treatment of heart failure. Clinical trials of VNS have produced mixed outcomes and very little is known about the mechanisms mediating the cardioprotective effects of VNS. This study has therefore implemented VNS in an ovine tachypaced model of heart failure, with the primary aim of quantifying its therapeutic effect in this model. Secondly, two potential underlying mechanisms of VNS have been investigated: 1) the effects of VNS on cellular calcium handling and 2) the effects of VNS on myocardial S-nitrosylation (S•NO).VNS treatment in this model of heart failure had a modest therapeutic effect. However, no differences in echocardiographic parameters, including those used as outcome measures in ongoing clinical trials, were observed between treated and untreated animals. Similarly, no differences in calcium handling parameters were observed between ventricular myocytes isolated from treated and untreated animals. Finally, VNS caused an increase in S•NO of several identified myocardial proteins when compared to untreated heart failure controls. However, this was a relatively small change compared to that observed between control and heart failure tissues. This data, as with studies before, highlights the need for a greater understanding of autonomic regulation and VNS in the heart failure setting, so that treatment strategies can be more effectively optimised. Given the limited therapeutic effect observed in this study, these potential mechanisms cannot be excluded as contributing to the cardioprotective effects of VNS observed in other studies.