A new method of scanning the heart using high resolution images and radioactive tracers could help identify people at highest risk of a heart attack.
The test, developed by researchers at the University of Edinburgh, can identify dangerous fatty plaques in the heart's arteries, which can lead to clots if they rupture.
The radioactive tracers seek out active and dangerous plaques, and when combined with high resolution images of the heart and blood vessels can provide a picture of the main danger areas.
Cardiologist Dr Marc Dweck told the BBC: "I suspect not all plaques detected will cause a heart attack, but it could be useful for identifying high risk patients who need aggressive therapy."
Findings could help doctors in deciding upon treatment for patients, whether it be prescription of drugs, suggesting lifestyle changes or offering medical procedures.
The new scan was tested on 40 patients who had recently had a heart attack, and highlighted the plaque which caused heart attacks in 37 of the patients, the study published in the Lancet medical journal revealed.
It is the first time a scan has identified danger zones, but further research is needed to discover if the detection of dangerous plaques before, rather than after, a heart attack can save lives.
Scientists will examine high-risk patients, including those who are about to have surgery.
Dr Dweck said if the scan or similar ones proved successful it would make a "massive difference".
He said: "Heart attacks are the biggest killer in the Western world and there is no prior warning, the first time people know about heart disease is when they have a heart attack.
"If we can treat and stabilise the plaques then we might be able to prevent heart attacks and stop people dying."
Professor Peter Weissberg, medical director at British Heart Foundation (BHF), said: "Being able to identify dangerous fatty plaques likely to cause a heart attack is something that conventional heart tests can't do.
"This research suggests that PET-CT scanning may provide an answer - identifying 'ticking time bomb' patients at risk of a heart attack.
"Nearly 20 years of BHF-funded research has led us to this point. We now need to confirm these findings, and then understand how best to use new tests like this in the clinic to benefit heart patients."
Thee are more than 100,000 heart attacks in the UK each year, according to the BHF.
Heart and circulatory diseases cause more than a quarter of all deaths in the UK, more than 159,000 each year.