The link does not appear to be influenced by other factors such as deprivation, high blood pressure or smoking status, and was not relevant for women.

Researchers from the Queen's Medical Centre, Nottingham, studied 673 male and 551 female patients at a rural general practice in the East Midlands.

They suggest there could be a number of explanations for the link.

Depression may lead to unhealthy lifestyles, such as failure to take exercise or an increase in smoking, which could increase strain on the cardiovascular system.

It is thought that some anti-depressant drugs can pose problems. Being depressed also impacts on the nervous system, with a knock-on effect on the heart, and can alter the balance of chemicals in the body.

Depression is also sometimes confused with the symptoms of tiredness, apathy and sadness which can occur immediately before a heart attack.

Undiscovered link?

Finally the researchers, writing in the British Medical Journal, postulate the possibility of an undiscovered link between heart disease and depression.

The reason that the link appears only to exist in men is unclear, although men appear to be more sensitive to chemical and nervous changes in the body.

The researchers also question whether GPs are less likely to diagnose depression in men unless it is particularly severe.

"If depression is a risk factor for cardiovascular disease then there could be a "dose response" relation whereby patients with severe depression have a higher coronary risk," they write.

The study also found that men with heart disease had an increased chance of depression after developing heart disease.