People are urged to eat oily fish at least twice a week

Eating oily fish like salmon or tuna at least twice a week could prevent a heart attack, a study suggests.

Doctors in the United States have found evidence to suggest that the omega-3 or n3 oils in this type of fish can stop dangerous irregular heart rhythms, which can trigger an attack.

The study is the latest to highlight the potential health benefits of eating oily fish or taking supplements.

Previous studies have shown that they can protect against heart disease and stroke.

Heart boost

Dr Alexander Leaf and colleagues at Harvard Medical School carried out tests on rats to find out exactly how these oils protect the heart.

They examined heart cells taken from unborn rats under the microscope. They found that these cells clump together and beat simultaneously and rhythmically just like a real heart.

They examined the effects of a variety of substances, including omega-3 oils, on these cells.

They found that the oils could prevent irregular heart beats. They believe the oils block excessive sodium and calcium currents in the heart.

These excessive electrical discharges can cause dangerous and erratic changes in heart rhythm.

Writing in Circulation, the journal of the American Heart Association, they said: "Animal experiments show that fatty acids from n-3 fish oils are stored in the cell membranes of heart cells and can prevent sudden cardiac death or fatal arrhythmias."

The doctors said their findings were backed up by previous studies. They pointed to one of the first studies to show that omega-3 oils can protect the heart, carried out in 1989.

In this study, researchers examined 2,033 men with heart disease who had been told to eat extra fat, fibre or fish.

They examined death rates among these men two years later. They found that death rates among those who had been told to eat fish were 29% lower than the other.

Dr Leaf said this suggested that the oils had helped to prevent irregular heart beats and, therefore, heart attacks.

Doctors believe that at least half of all heart attack deaths are caused by irregular heart beats.

Dr Leaf suggested that eating fresh or frozen oily fish is the best way of protecting the heart.

The British Heart Foundation recommends that everyone eats at least two portions of oily fish each week.