It was only when two army padres had come to his hospital bedside within an hour, and he had been told his wife was being flown to Londonderry to be with him, that Sergeant Major Steve Barrett began to realize how much his life was in danger.

He wasn't sure what had hit him. The attack was sudden and came almost without warning. But it wasn't an IRA bullet that had struck him down that morning in May. Barrett, only a few weeks past his 37th birthday, a 6ft 1in, 12-stone athlete who liked running marathons, had had a heart attack.

'I didn't believe it. I couldn't believe it. I still don't want to accept it', he says. 'You think: heart attack - finished. Well, I'm not finished'.

Yet Steve Barrett is a prime example of an epidemic that is increasingly worrying army doctors. Ten years of medical research has shown that the death rate from coronary heart disease among soldiers is twice that among their contemporaries in civvy street.

The average age of the casualties is just 40. Unlike Barrett, most of them die before they even reach hospital. For most survivors it is almost certainly the end of their army careers, so they suffer one huge psychological blow, rapidly followed by another.

Until recently, that is. The Army is now fighting to save its men, to avoid 'this shocking waste of manpower', as one senior medical officer puts it. To win, however, it has to identify the enemy, and then decide which tactics to employ.

'Why me?' asked Barret as he lay in hospital, and the Army is asking itself the same question. Why are so many of its men vulnerable to heart disease? And what can be done to protect them from more attacks?

Sergeant Major Barrett has not only survived but, just three months after his collapse, is back in uniform again. His career will continue; he has every chance of further promotion.

His return to active service has been made possible through what may seem a hazardous route. The tactics are, to say the least, unorthodox. But they offer hope to civilians as well as soldiers, and amount to a significant development in the after-care of coronary victims.

Six weeks after his heart attack, Barrett was transferred to the Army's cardiac rehabilitation unit at the Queen Elizabeth military hospital, in south London.

There, he was wired up to monitoring equipment, put on a treadmill, and exercised with increasing severity until he almost dropped from exhaustion - pushed, as the medical jargon has it, to his 'theoretical maximal aerobic capacity'.

Thereafter, he would be exercised to a pulse rate of 80 per cent of that maximum, to leave a safety margin.

That was only the beginning. What then followed, after a series of tests to assess the amount of damage his heart had suffered initially, was a three-week in-patient course of intensive, strenuous exercise, along with eight other patients.

The course involves a daunting daily program that might seem more appropriate as a training schedule for professional footballers rather than an aid to recovery from life-threatening illness.

From 8am until 6pm the patients go through a grueling series of physical work-outs on the hospital's sports field, in the gymnasium, and in the swimming pool. In the pool, for example, the requirement is to swim a total of 30 lengths, and tread water for a total of half an hour.

The grunts and gasps from the gymnasium floor tell their own story of weight-lifting, squats, sit-ups and static cycling'.

'If you haven't had a heart attack before the course, this is the place to get one', one observer jokes.

Barrett's rationale was only slightly different. 'If I'm going to have another heart attack, I want to have it here', he says, gulping air after a game of volleyball. 'But if I don't have it here, I'll have nothing to worry about anywhere else'.

Apart from relaxation therapy at the end of sessions, the only respite from the daily toil is a list of lectures on such topics as diet, smoking, exercise, the anatomy and physiology of the heart, and the causes of heart disease.

'The aim of these lectures is freedom from ignorance,' says Lt.-Col Peter Lynch, head of the hospital's cardiac department. 'Each man's worries from now on will all be justifiable'.

Lt.-Col. Lynch runs the rehabilitation unit and has produced the important research which has revealed how much soldiers are at risk. He investigated the deaths of soldiers from coronary heart disease over a period of 10 years, and showed that junior soldiers were twice as much at risk as comparable civilians. Then he began to look more closely at the factors involved in such cases.

Strenuous exercise, such as that undertaken by servicemen, was an unlikely cause, he found. Diet seemed irrelevant, since 53 per cent of soldiers are married and eat food similar to any other British household.

Stress peculiar to army life included moving house frequently, periods of separation from wife and family, and the dangers of serving in Northern Ireland. But all that had to be weighed against the security of employment and housing and the strong bonds of comradeship that the Army provides.

A family history of heart disease was no more common among soldiers than civilians. Lt.-Col. Lynch found that soldiers tended to be overweight and to have higher levels of blood cholesterol. These were two of the three main risk factors he identified.

But he was in little doubt that it was the third factor that was the deadliest enemy. Publishing his latest research in the British Medical Journal on June 22 this year, he wrote: 'The disproportionately high mortality from coronary heart disease in junior soldiers seems to be due to the high prevalence of heavy cigarette smoking in the British Army'.

The research showed that 95 per cent of soldiers with heart disease were consuming an average of 28 cigarettes a day. 'In the Army, the expected protective effect of physical fitness is overwhelmed by the deleterious effect of high consumption of cigarettes'.

In other words, Sergeant Major Barrett's marathon runs didn't have much impact on the 30 cigarettes he got through on most days. He'd been smoking since he was 15.

'It's the comradeship in the Army that makes you smoke so much', he says. 'You tend to share everything with your mates. Somebody's fag packet is always going round'.

Not surprisingly, Steve Barrett is now an ex-smoker. 'I've not had a cigarette since the day of my heart attack, and I don't miss them'.

At the end of his three-week course, Barrett and his fellow patients were given the Army's basic fitness test: a three-mile run, to be completed in a given time. It was a crucial stage; failure would have halted, at least temporarily, his return to uniform.

But, like most who go through the rehabilitation course, he passed. There will be a medical check-up in three months, and an annual follow-up.

'Very few of these men have been medically discharged from the Army and most have achieved a medical grading which allows them to function normally in their units and gain promotion in the normal way', says Lt.-Col. Lynch.

'Perhaps the most striking feature is the improvement in morale. Without exception, patients agree they now live much happier and more contented lives'.

But what of the basic problem, the coronary risk from cigarettes? Smoking has been as much part of a soldier's existence as spit and polish and NAAFI tea: since the First World War cigarettes have been seen as essential to the morale of the fighting soldier. Lt-Col Lynch is convinced that there must be changes in the tradition. 'Now that we know that the high mortality rate is because of heavy cigarette smoking, we have a much stronger case for asking the Army to provide vaporizers instead of cheap cigarettes”, he says.

Accordingly, he is submitting the latest evidence, along with such a recommendation, to the Army's top brass.