Two prominant human studies have shown tremendous benefit of fish oil supplementation for cardiovascular health. The largest study supplemented 18645 people with either 1800mg of EPA or placebo for a period of 5 years. The next largest study supplemented 11323 people with either 850mg per day of combined EPA and DHA or placebo for a period of 2 years. Both studies showed tremendously positive benefit from supplementation with fish oil.
The American Heart Association actively promotes intake of EPA and DHA. They state that through diet or through supplementation, intake of EPA and DHA are beneficial for cardiovascular health. This paper was published in 2003, and since this time a number of very important studies (including the study of 18645 people mentioned above) have been conducted. The next position statement of the American Heart Association will likely even more powerfully recommend intake of EPA and DHA.