How serious is the Prime Minister's heart problem? STEPHEN LEWIS investigates.

THOUSANDS of people in Britain suffer from heart problems like those which prompted Tony Blair's visit to hospital.

Cardiologist Dr Maurice Pye of York Hospital said it was likely the Prime Minister was suffering from one of two conditions, both of which could be loosely referred to as an 'irregular heartbeat'.

Supraventricular tachycardia is a condition in which the heart beats much faster than usual, but in a regular way. It is a hereditary condition. "But it is generally quite a benign condition, which is easily managed and treated," Dr Pye said.

The other possibility is that Mr Blair may have been suffering from paroxysmal atrial fibrillation, in which again the heart beats faster than usual (up to 200 times a minute) but this time irregularly.

This, said Dr Pye, is a more complex condition to deal with - but again, not life threatening.

Dr Pye said Mr Blair may have experienced symptoms ranging from mild discomfort in the chest to feeling faint and dizzy before being taken to hospital.

Professor Sir Charles George, medical director of the British Heart Foundation, said at hospital doctors would have taken blood from Mr Blair and carried out tests and he might have been given an injection to get his heart rate back to normal.

"But as he was there for five hours that suggests that wasn't successful and they might have offered electrical therapy, in which they give a shock across the chest as you would in a cardiac arrest," Sir Charles said. It would have been a small, controlled shock, and he might have been put to sleep for it and would not have felt anything."

Sir Charles said such heart problems were not uncommon in Britain, and often came without warning.

Dr Pye said that until further tests had been carried out, it would be difficult to be sure which of the two types of irregular heartbeat Mr Blair was suffering from.

But while it was possible Mr Blair may suffer further episodes, neither condition was life threatening, he said.

"It depends on which one he has got, and he will need a couple of days' rest," he said. "But I'm pretty sure it will have a minimal effect on his performance. It is not anything life threatening or debilitating, unless he gets frequent attacks that were occurring so often it was daily, which is very unlikely. There is no reason for him to stand down."

Inevitably, however, Mr Blair's condition will focus attention on the huge strains and stresses of being Prime Minister.

Mr Blair has always prided himself on being in shape, playing tennis and running on the treadmill to keep fit. He works out several times a week using the gym running machine, often exercising early in the morning.

Although looking older than when he first became to power, he has kept good health, and told saga magazine in an interview for his 50th birthday earlier this year: "I feel great, physically. I do more exercise today than I have done since I was at school."

His diagnosis of an irregular heartbeat is the first known problem since becoming Prime Minister in 1997.

Mr Blair has always piled pressure on himself, however - and even by his punishing standards, the last few months have been particularly gruelling, with the repercussions of the war with Iraq and the ongoing Hutton Inquiry into the death of weapons expert Dr David Kelly.

For much of this year the Prime Minister's face and body language have told the tale of someone under intense pressure, with the premier often looking haggard and careworn.

Although it is thought to be the first time Mr Blair has been taken ill since becoming Prime Minister, ill health has taken its toll on other top politicians.

Margaret Thatcher - like Mr Blair a workaholic - often boasted about her good health. But even she succumbed occasionally, once being taken ill with what looked like a bad bout of flu while in Sri Lanka.

Soon after leaving Downing Street she came close to collapsing while addressing a meeting in Chile, and later suffered a series of minor strokes.

Sir Winston Churchill fell ill during the latter part of his final term as Prime Minister, suffering a severe stroke in office - although the facts were kept from the public.

And Harold Macmillan suffered prostate rouble while he was Prime Minister.

The most tragic case recently, however, was John Smith, Mr Blair's predecessor as Labour leader. He died after a heart attack in May 1994, having suffered a heart attack a few years before from which he appeared to have recovered.

According to British Heart Foundation figures from 1999, abnormal heart rhythms such as those suffered by Mr Blair occur in 5 per cent of the male population in Britain, and in 3.9 per cent of men in Mr Blair's age range of 45-55. The condition is most common in older age ranges.

In women, the condition is slightly less common, occurring in 4.8 per cent of the population.

Updated: 12:09 Monday, October 20, 2003