Calcium contributes to the hard "plaque" deposits that fur up the walls of diseased arteries, causing them to narrow.
When this results in insufficient blood flow, it can lead to heart attacks.
Traditional methods of assessing heart attack risk involve totting up factors such as age, high blood pressure and levels of blood cholesterol.
The new research, published in the Journal of the American Medical Association, shows that adding a calcium score to the process significantly improves accuracy.
A US study on almost 6,000 patients found that the scans greatly improved the ability of doctors to identify high-risk individuals.
Dr Tamar Polonsky, of 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."