Marc-Vivien Foé , the former Manchester City and West Ham footballer who collapsed and died while playing for Cameroon on Thursday, may have been suffering from an undetected heart condition that might never have troubled him but for the extreme physical stress of the sport.

The second half of the Confederations Cup semi-final in Lyon, France, was well into the second half when the 28-year old Premiership player crumpled slowly to the ground in the centre circle. He had not been challenged by an opponent and there was no obvious reason for his collapse.

Cameroon were leading Colombia one goal to nil and the temperature was in the high 80s in the southern French city. Fellow players frantically signalled for help and Foe was carried from the pitch on a stretcher. He was declared dead after doctors had tried to resuscitate him for almost an hour.

Harry Redknapp, Foé's former manager at West Ham, expressed the shock felt throughout the soccer world. "Never have I seen someone in better physical condition than Marc," he said. That could have been the problem. One in 60 people is estimated to have an undetected heart defect, which in most people leading normal lives causes no problems. But in those with serious defects, about one in 500, who put their hearts under strain during sports, there is a higher risk of death.

The commonest defect is Cardiomyopathy, a genetic condition that causes thickening of the muscle in the heart wall, compressing the left ventricle and leaving no space for the blood to be pumped. It often affects young people who are physically active and may cause symptoms of increasing fatigue and tiredness over a year or more. Sportsmen and women often fail to read the signs, concluding that they must be unfit and need to work harder.

There is no cure for Cardiomyopathy but early treatment with drugs can prevent it. Barbara Taylor of the Cardiomyopathy Association said: "It often happens with sports people who are ultra-fit. They put their hearts under more strain than the rest of us."

Many non-sports people could live with the effects of the condition for many years without ever being aware of it because they never put their hearts under sufficient strain to cause problems, she said.

Cardiomyopathy was the cause of the death of Daniel Yorath, the 15-year-old son of Terry Yorath, a former international footballer and one-time manager of Wales, who collapsed during a kick around at the family home in 1994.

The following year, John Marshall, a top coach with the Football Association who trained Michael Owen, collapsed and died. He had been unwell for more than a year but had never been given an electrocardiogram (ECG) to check his heart, said Alison Cox, of Cardiac Risk in the Young (CRY), a charity campaigning for better screening of heart problems in those under 35.

Ms Cox, wife of the former tennis star Mark Cox, set up CRY after her son developed Cardiomyopathy. She said: "It was after John Marshall's death that the Football Association introduced ECG and echo cardiograms - an ultrasound test which can detect heart enlargement - for all its young players. We would like to see all serious athletes having the test. ... The trauma of these young deaths is terrible - it is very different from the ordinary death from heart disease in someone over 65."

There are at least 10 heart defects that may occur in the young. Athletes tend to have enlarged hearts because of their fitness regime and these can be confused by non-specialists with hearts enlarged by Cardiomyopathy. As well as genetic causes, viruses can trigger problems, but some ailments may develop spontaneously. Myocarditis, a lethal condition, is caused by a virus that, once it has found its way into the heart, is difficult to clear. The only treatment is bed rest.

Ms Cox said that in Italy all serious athletes were offered an annual fitness test. "They have virtually eliminated sudden cardiac deaths," she said.

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