Increased consumption of n-3 fatty acids reduces mortality from sudden cardiac death, indicating that such acids have anti-arrhythmic effects. We did electrophysiological testing in ten patients with implanted cardioverter defibrillators who were at high risk of sudden cardiac death. To assess their immediate effects on the induction of sustained ventricular tachycardia, n-3 fatty acids were infused. Such tachycardia was not induced in five of seven patients. Our findings show that infusion of n-3 polyunsaturated fatty acids does not induce arrhythmia, but did result in a reduction of sustained ventricular tachycardia in some patients.