Men's and women's hearts are different — in ways that doctors are still working to understand.

A recent government report adds more mystery: According to the federal Agency for Healthcare Research and Quality, or AHRQ, women are far more likely than men to be hospitalized for chest pain for which doctors can't find a cause.

In 2006, the latest data available, 477,000 women were discharged from US hospitals with a diagnosis of non-specific chest pain, compared with 379,000 men. That diagnosis is often given to patients who are admitted for a possible heart attack that turns out not to be one.

Heart disease is the number one killer of both sexes, claiming more lives each year than all cancers combined. More women than men have died from heart disease in the US every year since 1984, and they are twice as likely as men to die after a heart attack, according to the National Coalition for Women with Heart Disease.

But heart attacks often look different in women than men. While both frequently report chest pain, pressure or tightness, women more often have subtle signs instead, including dizziness, nausea, breathlessness, aches in the back, shoulders or abdomen, sudden weakness or fatigue or an overwhelming feeling of doom. A 2003 study found that 95 percent of women who had heart attacks started feeling some of those symptoms a month or more before.

"Women are very into their bodies — they know when they aren't feeling well," says Nieca Goldberg, medical director of New York University's Women's Heart Program. "That's the time to call your doctor, when there's still time to prevent a heart attack."

Could some of those non-specific chest pains in the AHRQ report have been early warning signs? There's no way of knowing, since the statistics don't track whether patients returned with a heart attack later.

It's also not possible to tell from the data how thoroughly each case of chest pain was evaluated for underlying causes like coronary artery disease, or CAD. Doctors long considered angina, a chest pain associated with CAD, to be a man's disease and have been slower to order tests for women. Indeed, the AHRQ data showed that in general, nearly twice as many men as women had angiograms and cardiac catheterizations, and nearly twice as many men were diagnosed with CAD.

But even when women do have such diagnostic tests, doctors are less likely to find CAD. "Women with chest pain are much more likely to have normal coronary arteries," says Rita F. Redberg, director of Women's Cardiovascular Services at the University of California — San Francisco School of Medicine. "The truth is, we don't always find out what causes it."

One theory is that some chest pain in women may be due to microvascular disease — blockages in tiny vessels that can't be seen on an angiogram. Such blockages are also too small to be opened with stents or angioplasty, but can be treated with beta blockers and nitroglycerine.

Given the growing awareness that heart attacks present differently in women, the AHRQ data may indicate that doctors are treating women with chest pain more proactively than they used to.

"Women's chest pain is increasingly taken more seriously — even if it's atypical — so doctors may have a lower threshold for admitting them," says cardiologist Edmund M. Herrold, a professor of medicine at the State University of New York-Downstate Medical Center in Brooklyn. "I think that's a good thing. In the past, women who should have been admitted were being sent home."

Should women think twice about getting help if they're having chest pain? "We're always trying to draw that line fine — not wanting people to ignore symptoms, but not thinking it's a heart attack everytime they get a twinge," says Dr. Redberg.

Studies show that women wait longer than men before going to the hospital — in part because the symptoms may be subtle, and in part because they don't want to "bother" doctors if nothing's wrong. But two-thirds of women who have heart attacks never make it to the hospital.

If you have any of the symptoms for more than a few minutes, seek help quickly. "Don't sit home and wonder," says Dr. Goldberg, who sometimes has to beg patients who call her in the middle of the night to go to the hospital.

She also suggests calling 911 rather than going on your own: "You'll get taken care of faster in the emergency room if you arrive by ambulance. The hospital can call the doctor for you."

Warning for Women

Chest pain is a common symptom in heart attacks, but women may instead have:

¦ Pressure or pain in shoulders, back, jaw or arms

¦ Dizziness or nausea

¦ Sudden fatigue or weakness

¦ Shortness of breath

¦ Unexplained anxiety

Source: The National Coalition for Women with Heart Disease