Doctors have been advised to prescribe oily fish or omega-3 fatty acid supplements to patients who have had heart attacks. The National Institute for Health and Clinical Excellence (NICE) believes that if doctors do so, and then if patients follow their advice, then they will be at a lower risk of suffering further heart attacks.

The guidance is the first time that NICE had advised patients to change their lifestyle, along with taking prescribed drugs, in order to avoid repeat heart attacks. The news has been welcomed by patient representatives which have said that the measures could have a big impact.

The new guidelines replace the ones set out six years and now advise patients to to give up smoking, be physically active for 20-30 minutes a day, and eat a Mediterranean-style diet. Professor Gene Feder, Chair of the Guideline Development Group, said that while drugs could make an enormous difference to patients who have had a heart attack, there is now also compelling evidence that lifestyle changes can play a role too.

The new guidelines recommend that patients who have a had a heart attack in the last three months should eat more oily fish or are prescribed certain preparations of omega 3 fatty acids. The recommendations come after research showed that one specific omega-3 supplement - Omacor - cut the risk of a patient dying suddenly by up to 45%.

Omacor is currently the only omega-3 supplement with a licence for post-heart attack treatment.

However, the costs of this to the NHS are likely to be quite high, as around 260,000 people have a first heart attack every year, and, of those, around a fifth may need supplements as they are intolerant to oily fish. NICE estimates the cost could be around 7 million pounds in the first year. Therefore it is recommended that those who can eat oily fish do so at least two to four times a week, as this not only prevents further heart attacks but also improves general health.

John Walsh, a patient representative on the Guideline Development Group, said: "There is really a lot of good advice in [the report] that we must ensure gets to patients. The changes that the average person needs to make are really quite small. In my case for example, I've decided that I'm not going to choose to live without cheese, but what I do now is eat very much less of it. I'm quite sure that from the patients' point of view, if we can get this information into their hands, and their minds and into their hearts, there will be a big health gain in this area."

Professor Mayur Lakhani, chairman of the Royal College of General Practitioners, said: "Having a heart attack used to be a life sentence for patients; now it is possible for most patients to lead healthy and fulfilling lives. This requires a high standard of modern medical care and for patients to follow lifestyle advice."