There are strong indications that eating (fatty) fish or n-3 fatty acids from fish reduces the risk of fata coronary heart disease (CHD). Observational studies in the general population show that consumption of moderate amounts of fish or n-3 fatty acids from fish are associated with a lower risk of fatal coronary heart disease and in particular sudden cardiac death. The most plausible hypothesis is that n-3 fatty acids reduce the risk of CHD mortality via anti-arrhythmic effects. Two clinical intervention trials show that prescription of fish or n-3 fatty acids to patients with prior myocardial infarction is effective in preventing mortality due to CHD. Ongoing trials will have to prove the effectiveness of a low dose of n-3 fatty acids and show that the underlying mechanism involves a protective effect against life-threatening arrhythmias. In addition to other recommendations for a healthier diet and lifestyle, consumption of one or two fatty fish meals a week is a highly effective and safe measure to reduce CHD mortality in both the general population and patients.