The British Heart Foundation (BHF) estimates as many as 50,000 Scots may have an inherited a genetic disorder affecting their heart health without realising it, as the charity calls for more research to help identify potentially deadly genes.
Someone living with an inherited heart condition has a 50-50 chance of passing it on to their children, but it could lie undetected for generations.
Each year across Scotland, around 50 apparently healthy people aged 35 or under are victims of sudden cardiac death with no explanation, devastating their families.
Launching its new campaign, the Fight for Every Heartbeat, charity stressed the need for urgent research into inherited heart conditions hidden within so many family trees.
Previous estimates suggested up to 32,000 Scots could be living with a faulty gene but BHF believes under-diagnosis means this figure may be much higher.
Despite advancements in research into inherited heart conditions many faulty genes still remain undiscovered.
Finding those genes is the first step towards developing improved genetic tests to find people at risk, said the charity, adding an early diagnosis can mean the difference between life and death.
Professor Peter Weissberg, medical director at the BHF, said: "We urgently need to accelerate research into inherited heart conditions.
"Over recent years researchers have made great strides in identifying some of the genes that cause inherited heart conditions. A genetic test in a child of an affected parent can save their life. More research is now urgently needed to identify all the genes responsible for these deadly disorders.
"Pinpointing genes which cause inherited heart conditions will allow affected children to be protected and, in the long term, will lead to new treatments to overcome the effects of the faulty gene."
Among the Scots who can identify with the dilemma facing carriers of faulty genes is Fiona Brown, from Dundee. The 38-year-old discovered she had a heart condition at the end of 2012 when she visited her GP for blood pressure tests, including an ECG. The tests revealed Fiona had Long QT, a condition that means a dangerous heart rhythm can be triggered by certain types of exercise or by shocks, including sudden noises.
Ms Brown's two children were subsequently tested for the condition. Her six-year-old daughter Abbey had not inherited the gene, but Ewan, now 10, had.
She said: "Getting my children tested was very emotional. It was frightening. In a way, you blame yourself.
"It's been a tough time getting my head around it, and I've been on a huge emotional rollercoaster - one day, I'm OK, the next, I'm scared. I have also had to deal with how my son has reacted to inheriting this condition from me and how this has affected him.
"We were an active, outdoor type of family, and we've now had to adapt our lifestyle accordingly. We've decided to let Ewan go swimming, but we send him off with concern every week. It's a balance between letting him live his life normally and enjoying the things kids enjoy doing, but as safely as possible. Ewan has been an absolute star. He just gets on with things and takes things in his stride.
"With something like Long QT, your heart can stop suddenly. There's no chance to say goodbye. So you have to make every day count."
Meanwhile, a study by Glasgow University has found that veterans who joined the armed forces in the 1960s and 1970s have suffered more heart attacks than their contemporaries who have never been in the military. However, younger veterans have a similar risk to the wider population.
Dr Beverly Bergman, a PhD student and former British Army soldier and senior military doctor, said: "There used to be a culture of heavy smoking and drinking in the Army, but improved physical fitness and health promotion initiatives within the forces, which really came to the fore from the late 1970s onwards seem to have contributed to improved health, hence the difference we see between the two groups.
"It emphasises the importance of not smoking. Veterans who smoke can really make a difference by giving up."