Abnormal autonomic activity has been shown to be a strong prognostic indicator of mortality in patients with heart failure (Nolan et al. 1998) and those who have had a previous myocardial infarct (La Rovere et al. 1998). Depressed heart rate variability and baroreceptor sensitivity are surrogate markers of impaired vagal tone associated with mortality in these conditions in which most of the deaths are sudden and due to ventricular arrhythmias, especially ventricular fibrillation (VF). We have recently shown that electrical stimulation of the vagus nerve in the neck ) has a strong anti-arrhythmic effect in the rabbit ventricle against VF. These effects are blocked in the presence of a nitric oxide (NO) synthase inhibitor providing indirect evidence that NO is involved in this effect. The implication of NO in mediating vagal activity in the ventricle is novel although