Doctors may be able to judge if someone is at risk of having a heart attack by looking for calcium in the arteries, research has shown.
Walls of the arteries are narrowed by hard "plaque" deposits, which can be made worse by calcium deposits.
Looking at factors such as age, high blood pressure and levels of cholesterol are traditional methods of assessing heart attack risk.
The new research, published in the Journal of the American Medical Association, shows that adding a calcium score to the process significantly improves accuracy.
Coronary Artery Calcium Score (CACS) is obtained by carrying out a computed tomography (CT) heart scan to reveal levels of calcium in artery walls.
A US study on almost 6,000 patients found that the scans greatly improved the ability of doctors to identify high-risk individuals.
Lead researcher, Dr Tamar Polonsky from Northern University in Chicago, said: "Almost one quarter of the people in the study who had heart attacks were considered intermediate risk based on traditional risk factors alone, but were considered high risk once we included their CACS."
An additional 13% of those patients who did not experience heart disease-related events were reclassified as "low risk" after the scans.