Women, especially younger women, are more likely than men to show up at the hospital with no chest pain or discomfort after having a heart attack - and they are also more likely to die than men of the same age, according to a US study.
That lack of symptoms can result in delayed medical care and differences in treatment, said researchers, whose findings appeared in the Journal of the American Medical Association.
"They might not even know they're having a heart attack,"said John Canto, from the Watson Clinic in Lakeland, Florida, who worked on the report.
He noted that while the results are based on a study of more than a million heart attack patients, they are still preliminary. But, he added, they do challenge the notion that chest pain and discomfort should be considered "the hallmark symptom" for all heart attack patients.
"If our results are in fact true, I would argue that rather than the one-size-fits-all symptom message, we also have to tailor that message to say that women less than 55 are also at higher risk for atypical presentation," Canto told Reuters Health.
Such "atypical presentation" can include symptoms such as unexplained shortness of breath, or pain in areas including the jaw, neck, arms, back and stomach.
Canto and his colleagues analyzed medical records in a national database of heart attack patients from 1994 to 2006, including about 1.1 million people treated at close to 2,000 hospitals.
They found that 31 per cent of male patients, and 42 per cent of female patients, didn't have any chest pain or discomfort. The likelihood of this sort of "atypical presentation"differed most between younger women and younger men, the researchers said.
Women also tend to be older than men when they have a first heart attack. In this study, the average age difference was seven years.
Women under 45 were 30 per cent more likely than men in their age group to present without chest pain. That dropped to 25 per cent between the ages of 45 and 65, and all but disappeared after the age of 75.
A similar pattern, with smaller differences between the sexes, was seen in the likelihood of death.
Almost 15 per cent of women died in the hospital after their heart attack, compared to about 10 per cent of men. Younger women with no chest pain were almost 20 per cent more likely to die than male counterparts.
But after age 65, the women's risk fell below that of men.
At least part of that difference could be due to lack of action by patients and doctors when symptoms are unusual, said Patrick O'Malley, an internist at the Uniformed Services University of the Health Sciences in Bethesda, Maryland.
"We tend not to think of heart disease in younger women if they're not having chest pain... and therefore we're not going to be as aggressive. It does delay treatment," he said.
"Because it's not chest pain, they'll be coming later,"added O'Malley, who did not take part in the study.
Canto said women, especially those who may be pre-disposed to heart attacks because they have diabetes, a family history of heart disease, or are smokers, should know that a lack of chest pain doesn't rule out the possibility of a heart attack - which researchers said was actually true for both sexes.