A simple and cheap blood test could warn people if they are at risk of suffering a heart attack within five years, researchers have said.
Scientists have linked high levels of antibodies produced by the immune system and a low likelihood of heart problems in the "exciting" research.
The new test looks for levels of IgG antibodies which appear to prevent a heart attack even if cholesterol and blood pressure levels are high.
IgG is found in all bodily fluids and protects against bacterial and viral infections.
The research, partly funded by the British Heart Foundation (BHF), studied more than 1,700 people at risk of heart attacks.
It found that those with the lowest levels of antibodies had the highest risk of heart attack.
During a five-year-trial carried out by researchers from Imperial College London and University College London, people with the highest number of antibodies were at least risk of suffering a heart attack or coronary heart disease.
Dr Ramzi Khamis, consultant cardiologist at the National Heart and Lung Institute, said: "Linking a stronger, more robust immune system to protection from heart attacks is a really exciting finding.
"As well as improving the way we tell who is at the highest risk of a heart attack so that we can give them appropriate treatments, we now have a new avenue to follow in future work.
"We hope that we can use this new finding to study the factors that lead some people to have an immune system that helps protect from heart attacks, while others don't. We also hope to explore ways of strengthening the immune system to aid in protecting from heart disease."
Coronary heart disease is the UK's single biggest killer, causing nearly 70,000 deaths each year.