Two teams of scientists have identified a genetic flaw which increases the risk of heart disease and heart attacks.
The genetic variant may account for one in five heart attacks
US and Canadian researchers found that up to one in four white people carries the section of DNA which increases the risk of heart disease by around 40%.
A separate study in Iceland found the same genetic variant was linked to a fifth of heart attacks.
Experts said the findings, published in Science, were important but lifestyle factors had a big impact on risk.
Both teams of researchers scanned the genomes of patients who had coronary heart disease or who had suffered a heart attack to see if there were any differences between them and healthy people.
The US/Canadian team found a section of DNA - called an allele - on a specific chromosome that was associated with heart disease.
Their study of 23,000 people, showed that those who carried one copy of this allele have a moderately increased risk of heart disease.
But people who have two copies, which accounts for about 20-25 % of white people, have a 30 to 40% higher risk of heart disease than individuals who carry no copies.
Professor Ruth McPherson, of the University of Ottawa Heart Institute, who worked on the study, said: "The effect is less than that of smoking or having a high cholesterol level.
"Nonetheless, screening healthy people for this genetic marker could provide information on future risk of heart disease and help identify those individuals who would benefit most from early applications of strategies to reduce heart disease risk."
The researchers will now check if the findings also apply to people from black and Asian ethnic minorities.
The Iceland study looked at the same stretch of DNA in 17,000 people.
They also found that more than 20% of people had two copies of the faulty allele.
People with both copies had a 60% increased risk of heart attack, compared with those who with no copies.
There have been other gene faults linked to heart attack risk. But having this genetic variant appears to confer a higher risk, and to be linked to around a third of cases in men under 50 and women under 60.
Dr Kari Stefansson, who led the research for the Decode genetics company, said if those at risk were identified, they could be given medications such as statins, or cardiac procedures - as well as healthy living advice - to reduce their risk.
It is still unclear why this particular area of the genome is linked to heart disease.
However, researchers believe it may be associated with hardening and narrowing of the arteries.
Professor Peter Weissberg, medical director of the British Heart Foundation, said: "Trying to find genes that put some families at an increased risk of heart attacks is like trying to find a collection of needles scattered amongst a field full of hay-stacks.
"The significance of these two studies is that two independent research teams have homed in on the same hay-stack.
"This makes it very likely that they are close to identifying a needle - an important gene in that region."
He added: "This will take a lot more research and - once found - the gene will be only one of several that are important. This research represents an important step along a very long journey, but a step in the right direction."