Excessive tiredness or trouble sleeping could indicate an impending heart attack in women, researchers say.
Excessive tiredness could be a warning sign
A study in the journal Circulation looked at more than 500 women who had suffered heart attacks.
About 70% had experienced unusually high levels of fatigue and 48% had reported disturbed sleep for more than a month before their attack.
The researchers said they studied women because they have higher death rates and higher rates of disease than men.
The study focused on women with an average age of 66 who had suffered a heart attack in the previous four to six months.
They were asked if they had experienced any of 33 early signs which can precede heart attacks, or any of 37 symptoms which can accompany one.
The women were also asked about other health problems, risk factors, medication and their social backgrounds.
About 95% of the women said they had experienced new or different symptoms more than a month before their heart attacks that did not continue afterwards.
Excessive fatigue and disturbed sleep were the most common symptoms.
In addition, 42% reported shortness of breath, 39% indigestion and 35% anxiety.
'Time for treatment'
Only 30% said they had experienced aching, tightness or pressure in their chests before they had a heart attack.
Forty-three per cent of women reported they did not even have chest pains during their heart attacks.
Professor Jean McSweeney of the University of Arkansas for Medical Sciences, told BBC News Online: "Women have a terrible time getting diagnosed, because they can suffer from quite vague symptoms."
She said she hoped the study would raise awareness.
"Since women reported experiencing early warning signs more than a month prior to the heart attack, this could allow time to treat these symptoms and to possibly delay or prevent the heart attack.
"Women need to be educated that the appearance of new symptoms may be associated with heart disease and that they need to seek medical care to determine the cause of the symptoms."
Prof McSweeney said both women and healthcare professionals needed to be aware that chest pain - usually assumed to be the primary sign of a heart attack - was less common that acute fatigue.
"Lack of significant chest pain may be a major reason why women have more unrecognized heart attacks than men or are mistakenly diagnosed and discharged from emergency departments.
"Many clinicians still consider chest pain as the primary symptom of a heart attack."
Belinda Linden, of the British Heart Foundation said the study "exposes the need for women to be aware of the wide range of possible symptoms of a heart attack such as chest and throat discomfort, breathlessness, sweatiness, weakness or dizziness.
"Tiredness, as a symptom, is important when it is severe or unusual.
"It may be as a result of one of several reasons including anaemia, chronic illness, infection, under-active thyroid, diabetes, medication effects or depression. "