And approximately one in three of these have suffered a heart attack without any knowledge of the episode.

Scientists at Glasgow University believe that the failure to detect heart disease means that thousands of people are exposed to the risk of a potentially fatal recurrence. Early treatment can cut that risk by around one third.

The number of people admitted to hospital with serious heart problems has risen by 50% in the past 10 years.

The researchers are developing a blood test that will reveal if a person has unknowingly suffered cardiac injury.

It will be will be used on patients at approximately 50 GP surgeries in the Glasgow area to ascertain whether it is effective at identifying heart problems.

The Glasgow team studied a random sample of patients aged between 25 and 74 registered with GPs in the city.

They found that 3% had suffered serious heart impairment, mainly heart attacks. Of those older than 50, the figure rose to 7%.

Half were unaware that they had suffered a heart problem.

Professor Henry Dargie, a clinical cardiologist at Glasgow University, said: "Considerably more people suffered from heart problems than we thought, and half seemed to have no symptoms at all.

"It is very important that these people are identified, not only to pinpoint the extent to which damage to the heart may require specific treatment, but also so that preventative measures can be applied."

No obvious symptoms

Cells try in vain to compensate after a heart attack

Professor Dargie said, despite exhibiting no obvious symptoms of heart disease, patients at risk often had tell-tale signs, such as high blood pressure and diabetes.

He said not only had a large proportion of people failed to recognise heart prolems, a significant number of those who had sought help were not receiving the best form of treatment, such as ACE inhibitors.

In a further study, Professor Godfrey Smith, of the Institute of Biomedical and Life Science at Glasgow University, found that cells in the uninjured part of the heart grow in response to the greater demands placed upon them by tissue death following a heart attack.

However, they are unable to cope with the extra demand and become progressively less effective, increasing the chance of another heart attack.

The new blood test for heart disease works by detecting a protein called brain natriuretic peptide that is released in large amounts by cells in hearts which have suffered serious damage.