Initial epidemiological, clinical trial and animal data have suggested that a diet high in omega-3 fatty acids reduces the risk of cardiac death and that this reduction in the risk was owing to the prevention of fatal arrhythmias. More recent data, however, suggest that, in some patients with heart disease, omega-3 fatty acid supplementation may increase the risk of potentially fatal cardiac arrhythmias and the risk of sudden cardiac death. Additional research needs to be carried out to confirm and characterize the proarrhythmic properties of omega-3 fatty acids and to determine their role in the treatment of patients with heart disease who have not had a recent myocardial infarction.