A blood test that could rule out a heart attack in under 20 minutes should be used routinely, say UK researchers.
A team from King's College London have tested it on patients and say the cMyC test could be rolled out on the NHS within five years.
They claim it would save the health service millions of pounds each year by freeing up beds and sending well patients home.
About two-thirds of patients with chest pain will not have had a heart attack.
A heart trace, called an ECG, can quickly show up major heart attacks, but it is not very good at excluding more common, smaller ones that can still be life-threatening.
Currently, patients with suspect chest pain and a clear ECG can have a different heart-attack blood test, called troponin, when they arrive at A&E. But it needs to be repeated three hours later to pick up signs of heart muscle damage.
Alison Fullingham, 49 and from Bolton, did not realise she was having a heart attack when she experienced pain in her upper chest, neck and jaw.
Despite a small change in her ECG, doctors initially suspected she was having a simple panic attack.
It was only hours later when her troponin tests came back that the correct diagnosis was reached.
Levels of cMyC (cardiac myosin-binding protein C) in the blood rise more rapidly and to a higher extent after a heart attack than troponin proteins, studies suggest.
That means doctors can use the new test to rule out a heart attack in a higher proportion of patients straightaway, according to the researchers who report their trial findings in the journal Circulation.
They carried out troponin and cMyC blood tests on nearly 2,000 people admitted to hospitals in Switzerland, Italy and Spain with acute chest pain.
The new test was better at giving patients the all-clear within the first three hours of presenting with chest pain.
Dr Tom Kaier, one of the lead researchers, funded by the British Heart Foundation (BHF) at St Thomas' Hospital, London, said: "Our research shows that the new test has the potential to reassure many thousands more patients with a single test, improving their experience and freeing up valuable hospital beds in A&E departments and wards across the country."
He says if the test were to be used routinely, it could provide doctors with reliable results within 15 to 30 minutes. It is only being used for research at the moment, however.
Dr Kaier's hospital carries out around 7,800 troponin blood tests each year. By his calculations, switching to cMyC would save his hospital £800,000 through reduced admissions. Extrapolate that to other NHS hospitals and the savings could be millions of pounds, he says.
Prof Simon Ray, from the British Cardiovascular Society, said more research was needed before the new test could replace the troponin test.
"Unlike currently available blood tests which need to be repeated at least three hours after pain it looks as though a single test is enough to make a confident decision on whether a patient has or has not suffered a heart attack. Not only can it be done earlier after the onset of symptoms but it also seems to be better at discriminating between heart attacks and other causes of chest pains. This is very important."