Doctors say thousands of lives could be saved by a test which can predict who is in the early stages of a heart attack.
A heart attack happens every two minutes in the UK
It means that doctors in A&E would be able to tell which chest-pain sufferers are likely to have cardiac arrests.
Doctors writing in the New England Journal of Medicine say it could also be offered as part of heart check-ups by GPs.
Tests are available now, but none are reliable predictors of who is at risk.
Someone suffers a heart attack every two minutes in the UK.
The new test checks for levels of an enzyme called myeloperoxidase (MPO), which is made in white blood cells.
It is produced when the arteries become inflamed and fatty deposits build up which can rupture and create large blood clots which can clog major vessels, causing heart attacks or strokes.
Researchers from the Cleveland Clinic tested 604 A&E patients who had complained of chest pains.
Those with the highest levels of MPO in their blood were found to have four times more likely to have a heart attack within two months.
When the results were combined with a second test, which measures the amount of the heart muscle protein troponin in the blood, it was possible to identify 85% of those at risk.
The troponin test is one of a range of checks currently available, but they are often unreliable predictors of heart attack risk.
Dr Eric Topol, who led the research, said: "You can tell a patient he did great (on a conventional test), and a week later he drops dead.
"There's always been something missing."
Dr Richard Stein of the Weill Cornell School of Medicine in New York said the MPO test was very inexpensive and easy to measure.
"It's the first simple blood test that will allow us to take a patient who comes into the hospital with chest pain and say whether he's in the early stages of a heart attack or if he's at risk of having a heart attack in 30 to 60 days."
Belinda Linden, of the British Heart Foundation said: "Recent evidence suggests that inflammation of the arteries is an important indicator of future heart attacks and strokes.
"Several indicators of inflammatory activity in blood vessels have provided early information about the risk of coronary heart disease.
"It is important to note that this test is still being trialled and further tests are required before it is considered a reliable measure of an impending heart attack. However, a test that can clarify any increased risk would, in principle, be welcomed."