Doctors could better predict which patients are likely to have a heart attack by testing blood for fish fats, according to US research.
Heart attack risk is higher if fish fat blood levels are lower
A Harvard University expert said those at highest risk have low levels of omega-3 fats - found in fish oil.
But British heart experts said a chat about diet would be as helpful.
The research was presented to the International Society for the Study of Fatty Acids and Lipids congress in Brighton.
Low levels of certain types of omega-3 fats in the blood are known to increase the risk of a possibly fatal heart attack.
Scientists have also known for some time that eating oily fish protects the heart and reduces the risk of a heart attack.
Although they do not know exactly how, mounting evidence suggests they have a stabilising influence on the heart.
Dr Albert and colleagues say checking omega-3 levels could save lives by alerting doctors to which patients are at high risk of heart attacks and sudden cardiac death.
This would allow them to intervene earlier.
Dr Albert said: "If blood levels of the long-chain omega-3 fatty acids form less than 4% of the fatty acids in red blood cells, risk of death from a heart attack is at its greatest compared with a level of 8% when risk is at its least."
Dr Ray Rice from the International Society for the Study of Fatty Acids and Lipids said: "This work opens up the possibility of a simple blood test to identify those people at high risk of death from a heart attack, and brings with it the relatively simple preventative solution of increasing omega-3 intake to prevent an attack."
Belinda Linden, head of medical information at the British Heart Foundation, said: "Dr Albert's comments support the clear evidence that eating oily fish rich in omega-3 fats can provide protection against cardiovascular disease.
"However, as blood levels of omega-3 are a direct reflection of fish consumption, it is unlikely that a blood test would be any more beneficial in helping to assess heart health than a discussion about diet between patient and doctor.
"Seven out of 10 people in the UK still don't eat enough fish.
"By eating a balanced diet containing fish, fruit and vegetables, and low in salt and saturated fats the chances of developing coronary heart disease, the UK's single biggest killer, are significantly reduced."
Earlier this week, the Food Standards Agency issued advice on how much oily fish it is safe for people to eat.
Oily fish contains omega-3 fatty acids which help to prevent heart disease, but pollutants in the fish may also pose a health risk to human health.
It says men, boys and women past childbearing age can eat up to four portions of oily fish such as salmon, tuna, trout and sardines a week.
Women of childbearing age should keep to a maximum of two portions a week.