The early morning rap on the door and the police car parked in the street outside.  As she went downstairs, Natalie Cutler realised on that bleak early January morning that something awful must have happened. 

"I just knew," says Natalie, sadly. 

"I heard the bang on the door.  It was 4am.  I came downstairs.  There were two police officers.  I didn't want to hear what they'd come to say.  I didn't want them to tell me which one it was. 

Her first thought was that something must have happened to one of her three strapping sons.  Tragically, she was right. 

"One of them said, 'Natalie Cutler, do you have a son called Stuart?', she recalls.  "It was awful .... just awful." 

Natalie pauses, takes a deep breath and remembers through falling tears the nightmare of learning how Stuart, 22 years old, fit, apparently healthy and just weeks earlier the life and soul of the family's Christmas celebrations, was one minute in the kitchen getting a glass of water, and the next, dead. 

"We were told he was probably dead before he hit the floor," explains Natalie, 52.  "It didn't matter that the ambulance was at the house within eight minutes and that they spent 20 minutes trying to revive him.  He was already gone." 

There was, the family later learned, nothing that anyone there could have possibly done.  His heart had simply stopped.  Yet had Stuart - one of at least 12 young people to die in similar circumstances every week - undergone two simple, non-invasive checks, then perhaps his early death could have been avoided. 

It's why today Natalie and a group of families from around Scotland who have also been left to cope with the shock of losing loved ones, will head to the Scottish Parliament to launch a fresh appeal for every young person in the country to undergo heart screening. 

At the root of the campaign, led by charity CRY (Cardiac Risk in the Young) will be a powerful postcard featuring the faces of 12 young Scots - among them Stuart - each one of them cut down by a previously undetected yet often preventable heart condition. 

Sadly, points out Natalie, each poignant portrait represents what seems to be a growing and tragic problem.  For the number of young people who lose their lives to sudden cardiac death - often described as Sudden Adult Death Syndrome (SADS) - has leapt 50 per cent from previous estimates. 

For most - around 80 per cent - there will have been no warning, no previous symptoms and no hope of surviving. 

"It's awful to think there are around 16,500 young people in Scotland walking around right now with an undiagnosed heart condition.  Some might die tomorrow or next week, next year," adds Natalie, a project manager for a telecoms company. 

"And what's also really shocking is that the equipment is there that can help save their lives.  It just isn't being used." 

It was January 17, 2009. just weeks after Stuart had travelled home to mid Calder from Cheshire where he had set up home with his girlfriend. 

"It was lovely to have him home, recalls Natalie, 52.  "I got to be 'mummy' again and I loved it." 

Stuart had been sitting at home watching a movie with girlfriend Becky, the couple's cat snoozing on his knee, when he complained of slight palpitations. 

"He told Becky he had this strange feeling," Natalie recalls.  "He felt his heart racing." 

While Stuart's girlfriend went to call her mum to ask for advice, he walked to the kitchen to get a glass of water.  She heard the glass smash.  He'd collapsed.  When she rushed through she though he'd passed out and phoned 999.  It turned out he was already dead before he hit the floor. 

The family was later told Stuart had an enlarged heart, a treatable condition which he had either been born with or had developed as a youngster. 

While Natalie and husband David, 58, wrestled with their grief, there was also panic that their two other sons, Michael, 30 and Richard, 27, might also be affected.  The brothers underwent emergency tests.  Luckily, both were clear. 

"But for Stuart, it was a ticking time bomb in his chest," she adds.  "It's terrible to think that he died of an undiagnosed heart condition, which, had it been found earlier, then something could have been done." 

That's the case in 90 per cent of sudden cardiac death cases, and the reason why CRY is relaunching its original 2007 appeal for a national heart screening programme for young people.  Back then its hard-hitting poster featured eight young people's portraits to represent the number of deaths each week from previously undiagnosed cardiac conditions.  But new figures - perhaps the result of greater awareness and post mortem tests - show the number of cases every week is closer to 12. 

CRY's chief executive, Alison Cox, says: "As the recorded incidence of sudden cardiac death rises it is timely for us to return to Scotland to re-launch this powerful campaign as a way of emphasising the importance of screening. 

"These 12 faces are just a snapshot of the problem.  We need to keep up the pressure and engage support from as many MSP's and MPs as possible to ensure we are doing everything we can to prevent other families from experiencing tragedies." 

CRY wants the Scottish Government to extend an existing cardiac screening programme, which provides ECG and echocardiograph tests for elite athletes.  It was launched in 2008 following the death from heart failure of Motherwell FC captain Phil O'Donnell, 35. 

Natalie adds: "An ECG takes just 20 minutes and an echocardiograph about the same.  So 40 minutes of testing on equipment that's already there could help save so many lives.  It's just awful when you know a simple test could be all that's needed." 

WORLD UPSIDE DOWN

Cricket captain James Green was in the middle of a cricket match in the Meadows when he suddenly collapsed and died. 

The newlywed was playing for Marchmont Cricket Club's first team in a league fixture.  He was in the midst of organising players between overs when, out of the blue, he dropped to the ground.  He was 34. 

Wife Shelagh recalls: "James and I finally got round to getting married in November 2011.  Six months later James went off to play cricket and didn't come home. 

"He was rushed to nearby Edinburgh Royal Infirmary - when I arrived the medics had been trying to revive him for some time, but without success.  My handsome, witty, intelligent 'other half' was gone. 

"As you can imagine, that sort of thing turns your world upside down in an instant." 

James, who lived in Easter Road, worked as an analyst for Scottish Natural Heritage.  Within months of |joining the Marchmont club he'd made a mark as a prolific wicket taker and highly accurate bowler and risen to become its captain. 

His loss is understood to be the result of arrhythmogenic right ventricular cardiomyopathy, was a second tragedy to hit his family.  For James' cousin Rupert had collapsed and died in similar circumstances eight years earlier while playing tennis. 

Too much of a coincidence, further investigation suggested a genetic link -particularly as James and Rupert's mothers were identical twins. 

"At the same time as losing a son, brother and husband we were dealing with the implications for the remaining family," recalls Shelagh, now one of charity CRY's county representatives, offering support and help to other families affected by sudden death. 

James is amongst the 12 people featured on the CRY poster highlighti8ng the number of people who die in Scotland every week from undiagnosed and often preventable cardiac problems. 

"Three of my brother-in-laws and one of my sister-in-laws have ICD's fitted, cousins are also being treated and my gorgeous little nieces and nephews are being monitored. 

"The loss of James and Rupert and the subsequent knowledge that has given the family, means we are hopeful our families won't experience the agonies of the sudden and untimely loss of a young person again."