Patients who have had a myocardial infarction (MI) should eat at least 7g of omega 3 fatty acids from two to four portions of oily fish a week, according to NICE.
It published updated NICE guidance on secondary prevention of MI published last week.
For those who cannot tolerate oily fish, NICE recommends prescribing a 1g daily supplement of omega 3 for up to four years, but only if the MI was within the last three months.
Gene Feder, chairperson of the guideline development group, said: "The benefits of omega 3 have been mooted before but not in such a specific way.
"This is new in terms of NICE guidance and we are confident about the three-month window," he said.