The study found that the patients with the longest clot lysis time had a 40 per cent increased risk of recurrent myocardial infarction.
A new blood test could identify patients who are at higher risk of developing cardiovascular disease after suffering a heart attack, scientists say.
The research published in the European Heart Journal may help scientists to identify new targets for reducing the risk and eventually lead to more effective treatments.
Researchers, led by Professor Rob Storey from the University of Sheffield in the UK, analysed blood plasma samples from more than 4,300 patients with acute coronary syndrome as they were discharged from hospital.
They measured the maximum density of a clot and the time it took for the clot to break down - known as clot lysis time.
The study found that the patients with the longest clot lysis time had a 40 per cent increased risk of recurrent myocardial infarction or death due to cardiovascular disease.
"We have made huge strides over the last two decades in improving prognosis following heart attacks but there is still plenty of room for further improvement," said Storey.
"Our findings provide exciting clues as to why some patients are at higher risk after heart attack and how we might address this with new treatments in the future," he said.
The results showed novel therapies targeting fibrin clot lysis time may improve prognosis in patients with acute coronary syndrome.