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Conventional wisdom has it that heart attacks come out of the blue. We're also trained to expect a heart attack to happen a certain way; the victim clutches his chest, writhes in pain, and collapses. But for women, it often doesn't happen that way. Study after study shows heart attacks and heart disease are under-diagnosed in women, with the explanation being that they didn't have symptoms.

But research shows that's not the case. Women who've had heart attacks realize, looking back, that they experienced significant symptoms -- they just didn't recognize them as such.

In a study funded by the National Institutes of Health and published in Circulation: Journal of the American Heart Association, 95 percent of women (that's almost all!) who'd had heart attacks reported experiencing symptoms that were decidedly new or different from their previous experience a month or more before their attacks.

Even when a heart attack is occurring, women are often slow to realize what's happening and call a doctor. The reason? Women's heart attack symptoms are different than men's. This failure to recognize heart attack signs in women has led to a grim statistic: Women are more likely to die from sudden cardiac death than men are, and two thirds of women who have a heart attack don't recover completely.

To prevent a heart attack from sneaking up on you, watch for these 7 little-known signs of heart attack:

1. Fatigue. More than 70 percent of women in the NIH study reported extreme fatigue in the month or months prior to their heart attacks. This was not just your run-of-the-mill tiredness -- the kind you can power through -- this was an overwhelming fatigue that sidelined them from their usual schedules for a few days at a time.

2. Sleeplessness or Insomnia. Despite their fatigue, women who've had heart attacks remember experiencing unexplained inability to fall asleep or stay asleep during the month before their heart attacks.

3. Anxiety and Stress. Stress has long been known to up the risk of heart attack. But what women report is the emotional experience; before their heart attacks they felt anxious, stressed, and keyed up, noticeably more than usual. Moments before or during a heart attack, many women report a feeling they describe as "impending doom;" they're aware that something's drastically wrong and they can't cope, but they're not sure what's going on.

4. Indigestion or Nausea. Stomach pain, intestinal cramps, nausea, and digestive disruptions are another sign reported by women heart attack patients. Become familiar with your own digestive habits, and pay attention when anything seems out of whack. Note especially if your system seems upset and you haven't eaten anything out of the ordinary.

5. Shortness of Breath. Of the women in the NIH study, more than 40 percent remembered experiencing this symptom. One of the comments the women made is that they noticed they couldn't catch their breath while walking up the stairs or doing other daily tasks.

6. Flu-Like Symptoms. Clammy, sweaty skin, along with feeling lightheaded and weak, can lead women to wonder if they have the flu when, in fact, they're having a heart attack.

7. Jaw, Ear, Neck, or Shoulder Pain. While pain and numbness in the chest, shoulder, and arm is a common sign of heart attack (at least, among men), women often don't experience the pain this way. Instead, many women say they felt pain and a sensation of tightness running along their jaw and down the neck, and sometimes up to the ear, as well. The pain may extend down to the shoulder and arm--particularly on the left side--or it may feel like a backache or pulled muscle in the neck and back.

In addition to the symptoms they do have, women differ from men in another significant way -- they may not experience many of the symptoms we traditionally associate with heart attacks. This, experts say, is a major reason why women's heart attacks go unrecognized and untreated. Almost half of all women in the NIH study felt no chest pain, even during the heart attack itself. Numbness is another symptom women may not experience, experts say.

How to protect yourself or the women you care about?

If your body is doing unusual things and you just don't feel "right," don't wait. Go see your doctor and ask for a thorough work-up. And if you have any risk factors for cardiac disease, such as high blood pressure, high cholesterol, smoking, or family history of heart disease, mention these to the doctor. Time is of the essence, so don't count on medical staff to know your background or read your chart -- tell them your risk factors right away, so your condition can be evaluated fully and completely.