There are virtually no cognitive and systemic side-effects associated with vagus nerve stimulation (VNS), which makes it a valuable treatment modality for patients with a poor tolerance to antiepileptic drugs. The safety of VNS therapy have been established in clinical studies, but there are few reports on the cardiac side effect associated with the intraoperative lead testing for implantation of the device for VNS. We report a patient with refractory epilepsy who experienced a complete atrioventricular block intraoperatively as a result of inadvertently high current intensity during the initial testing for implantation of a left vagus nerve stimulator.