The researchers compared blood samples from heart attack patients and healthy people.

This revealed differences in cells that lined the inside of the arteries before breaking off into the bloodstream.

In the heart-attack patients, these circulating endothelial cells were much more numerous and abnormally large and mis-shapen, the journal Science Translational Medicine reported yesterday.

The researchers believe the difference should be noticeable when the artery is cracking, making it possible to predict a heart attack.