Aisha Dodwell knew that something wasn't right with her baby boy, but the doctors seemed to disagree. She had taken Rio to the GP on successive occasions, but was told he was suffering from a viral infection that would get worse before it got better.

'He looked so ill I decided I would take him to casualty, but as we stepped out of the front door he suddenly stopped breathing,' she recalled. 'I managed to resuscitate him for a few seconds, but then he stopped again and the paramedics couldn't save him.'

Aisha now has another child, five-month-old Ella Rae. Her grief is still overwhelming and there is the nagging uncertainty about the real cause of Rio's death. A post-mortem told them it was myocarditis, an inflammation of the heart muscle, but they don't know what caused it. 'It doesn't explain much to us,' said Dodwell, from north London.

She and Rio's father, Graham Idahen, were yesterday attending an annual support day organised by the charity Cardiac Risk in the Young for families who have suddenly lost a child or relative to a heart defect. The Observer was the first newspaper allowed in to talk to families who had travelled from around Britain to find out more about their own individual tragedies as well as talk to experts and counsellors.

As many as eight people a week die unexpectedly from cardiac problems, but the NHS is badly equipped to give the survivors the support and information they need. Many of the bereaved spend months, if not years, trying to find out the exact nature of the illness; they face a much tougher problem attempting to ascertain whether their other children may be at risk.

There is no national genetic testing centre in Britain for families most at risk from sudden cardiac death. Many of the genes have been detected, yet the NHS cannot offer any service to test the survivors. The only families who receive the tests are those where doctors, as part of their research, can send blood samples to Denmark or Italy.

Very lucky families make it to Professor Bill McKenna, one of the world's leading experts in sudden death syndrome, the name for a collection of conditions which cause cardiac death. Hypertrophic cardiomyopathy, an unexplained thickening of the heart in young adults, carries a 1 per cent annual risk of sudden death. This genetically transmitted disease affects one in 500 adults and is the commonest cause of sudden death in otherwise fit young people.

Yet, despite the fact that there are effective treatments to prevent these deaths, there is no targeted provision in the healthcare system to manage this. Families with these problems are not being systematically referred to specialists or properly evaluated. They are not told that youngsters who enjoy a lot of sport are particularly at risk.

'If we could get to these families, we could forewarn them of the risk, then look at treatments for them, such as drugs or pacemakers,' said McKenna, professor of cardiology at University College London, who runs a clinic from the Heart Hospital.

He is scathing of the government's unwillingness to set up a proper system of referral to experts and evaluation for families. 'It's crazy that we've detected some of these genes and can't test those families most at risk. It would even help if GPs took a proper family history, because then you could probably pick up around half of those in most danger of sudden death.'