Alterations of autonomic tone appear to have important effects on the electrical stability of the heart. Since altered electrical stability, ventricular fibrillation, is the cause of death in the majority of patients who die from ischemic heart disease, the effects of the autonomic nervous system on ventricular electrical stability have been examined. Increased vagal tone increases the electrical stability of the heart and reduces the incidence of spontaneous ventricular fibrillation after coronary occlusion. These salutary effects of increased cholinergic tone appear to be mediated by cholinergic innervation of the ventricular conducting system. Conversely, increased adrenergic tone decreases the electrical stability of the heart and increases the propensity of the heart to develop ventricular arrhythmias during coronary occlusion. The interaction of the adrenergic and cholinergic system during myocardial ischemia may be one of the important determinants of survival in patients with coronary artery disease and acute myocardial infarction.