File picture: Valentin Flauraud/Reuters A blood test could spare heart patients repeat heart attacks.

One in five heart attack sufferers will have another episode within 12 months, despite treatment with aspirin and other anti-clotting medicines.

While these drugs are proven to reduce the chances of another attack, side effects can including bleeding in the stomach and, in rare cases, the brain.

But now scientists believe they have discovered the ‘sweet spot’, minimising the potentially-catastrophic risk of both while preventing more heart attacks, which occur when a blood clot forms in a major artery, cutting off the blood supply to the heart.

Researchers from the University of Sheffield, whose findings were published in the European Heart Journal, analysed blood from more than 4,300 patients discharged from hospital.

They measured the density of a blood clot and the time it took for it to break down – known as clot lysis time. Those that took the longest were nearly twice as likely to die from a heart attack within a year.

By using their new test, doctors can give bigger doses for people at the highest risk, but reduce unnecessary medication for those who do not need it.