Animal and in-vitro studies have shown profound antiarrhythmic effects of n-3 polyunsaturated fatty acids (PUFAs) on the heart. Because n-3 PUFAs (in particular docosahexaenoic acid) are abundant in nervous tissue, this antiarrhythmic effect may be mediated by effects of n-3 PUFAs on autonomic control or tone. This paper reviews the effect of n-3 PUFAs on heart rate variability, a noninvasive indicator of cardiac autonomic function. In most, although not all, studies, dietary n-3 PUFA levels and n-3 PUFA supplementation are related to improved heart rate variability. Although further research is required to confirm these relationships, the results support a beneficial effect of n-3 PUFAs on autonomic tone in humans, specifically an increase in vagal tone, which may reduce the risk of arrhythmias. The modulation of heart rate variability by n-3 PUFAs may partly explain the reduction in sudden cardiac death observed in subjects with a regular intake of n-3 PUFAs.