Largely initiated by studies among Eskimos in the early 1970s, great attention has been given to possible effects of omega-3 polyunsatured fatty acids (PUFA) in cardiovascular diseases. A series of positive effects on pathogenetic mechanisms of cardiovascular disease has been discovered from laboratory studies in cell cultures, animal models and in humans. omega-3 PUFA can reduce platelets and leucocytes activities as well as plasma triglycerides. Moreover they can have antiarrhythmic properties. Nowadays patients who experienced myocardial infarction have decreased risk of total and cardiovascular mortality by treatment with omega-3 PUFA (1 g daily). This effect is present irrespective of high or low fish intake or simultaneous intake of other drugs for secondary prevention of coronary heart disease. Mainly on the basis of GISSI Prevention trial results, dietary supplementation with omega-3 PUFA is now recommended as a new component of secondary prevention after myocardial infarction in national and international guidelines.