Thousands of people suffer from "silent" but potentially deadly heart attacks every year, as we confuse them with indigestion, a pulled muscle or flu.
Researchers have found silent heart attacks are almost as common as the standard attacks that prompt hundreds of thousands of hospital admissions a year.
The American team also discovered women who suffer a silent attack were 58 per cent more likely to die within a decade, while in men the risk rises by 23 per cent.
They occur when the blood flow to the heart is temporarily blocked - as with a normal heart attack - causing potentially fatal damage and scarring. But many patients either show no symptoms at all or assume they have indigestion, the flu or a strained muscle.
Experts believe many deaths occur in patients who have previously suffered a heart attack without knowing.
Dr Zhu-Ming Zhang and other researchers from the Wake Forest School of Medicine in North Carolina studied the records of 9,498 middle aged men and women.
Over ten years 7.4 per cent suffered a heart attack, and in 45 per cent of cases they were silent.
Dr Zhang said the study shows silent heart attacks, or silent myocardial infarctions (SMIs), are just as common as ordinary ones.
She added: 'Given that SMI is characterised by no or mild symptoms, those patients are deprived from medical treatments that could prevent subsequent adverse outcomes'.
Conservative estimates by the British Heart Foundation show at least 20,000 Britons suffer a silent heart attack each year, while about 83,000 have a regular attack.
Professor Jeremy Pearson, Associate Medical Director at the British Heart Foundation, said:
"This study emphasises that individuals who have ECG scan results which suggest a heart attack, but who don't have any classical symptoms, should be investigated more fully to determine their need for future treatment."