FRESNO, Calif. — Vicki Westburg made excuses for being tired and short of breath.

She blamed long, stressful days on her job as a special education administrator for a weariness she couldn't shake. And she thought her labored breathing was because of asthma.

When she woke gasping for breath on New Year's Eve a year ago and her husband rushed her to the hospital, Westburg, 48, of Fresno, Calif., suspected an asthma attack.

Instead, she was stunned: Tests showed congestive heart failure.

Westburg is among 8 million women nationwide diagnosed with heart disease — and that doesn't include many others who don't even realize they have it.

Heart disease is the No. 1 killer of women in the United States, claiming the lives of more women each year than men. But in doctors' offices across the country, heart disease in women often goes undiagnosed. Their symptoms don't mirror those seen in men, and women tend not to recognize the warning signs, doctors say.

Silent killer

We expect men to die of heart disease. But it has been killing more women nationwide than men each year since 1984, and the gender gap shows no signs of going away.

The number of women who die from breast cancer and all other forms of cancer combined doesn't equal the death toll from cardiovascular disease, including heart attacks and strokes, according to the American Heart Association.

This year, an estimated 490,000 women nationwide will die of heart disease.

Nearly half of women who have a heart attack had never been diagnosed with heart problems, according to a June 2006 program brief on women's cardiovascular health by the federal Agency for Healthcare Research and Quality.

The agency cited a review of medical records of 150 Minnesota women who suffered heart attacks between 1996 and 2001.

The women had made 8,732 visits to doctors and had 457 hospitalizations in the 10 years before their first heart attacks, the report said. Doctors diagnosed only 52 percent with heart disease before they had heart attacks.

Misleading symptoms

Women's symptoms don't make it easy for doctors to detect heart disease.

In men, chest pain or pain in the arm or jaw are classic signs of coronary artery disease, which can lead to a heart attack when an artery is blocked. In women, those signs might not be present.

Even when women with coronary artery disease exercise, "they may not get the typical chest pain," said Dr. John Telles, a Fresno cardiologist.

Instead, women can have an array of subtle symptoms: unusual tiredness, anxiety, problems breathing, indigestion, trouble sleeping. These can be mistaken for other ailments. Doctors are still trying to understand why women have different symptoms.

But without chest pain to warn them, women might not seek treatment for heart disease until it's an emergency.

Emergency room doctors fail to diagnose about 2 percent of patients with heart attacks because they don't have typical symptoms, according to the Agency for Healthcare Research and Quality. The misdiagnosed patients tended to be women younger than 55 or minorities reporting shortness of breath instead of chest pain, the agency said.

Inequalities

Doctors are trying to understand why heart disease kills more women than men.

The American Heart Association says 77 percent of women age 40 and older — compared to 82 percent of men — survive a year after a first heart attack.

One reason doctors suspect for the difference: Women's heart disease often has progressed by the time they are treated for it. And the longer heart disease goes undetected and untreated, the greater the risk of complications from procedures or surgery.

But research also suggests women receive fewer standard drugs for their heart disease than are prescribed for men and that they also have fewer procedures and operations to open clogged arteries.

An analysis of 327,040 men and women who had had heart attacks found women were less likely to receive drugs — aspirin, beta-blockers, intravenous heparin or nitrate therapy — during the first 24 hours in a hospital.

The women also were less likely to get angiography to examine blood vessels and angioplasty, a balloon procedure to open them. They also were less likely to have coronary bypass surgery than men, according to the Agency on Healthcare Research and Quality. And the women were more likely to die while in the hospital, the agency said.

"Women tend to be underdiagnosed, undertreated and have higher complication rates in therapy than we see in men," said Dr. John A. Ambrose, chief of cardiology at the University of California at San Francisco-Fresno Medical Education Program.

Operating on women with advanced coronary artery disease can be technically challenging, said Dr. Richard Gregory, medical director of cardiothoracic services at Community Regional Medical Center and Fresno Heart & Surgical Hospital.

Women's hearts, valves and arteries are smaller than men's. And the chest area is smaller, giving doctors less room to work during open-heart surgery, he said.

Emotional toll

Living with heart disease isn't easy. Ongoing struggles with fatigue and shortness of breath reduce the quality of life.

And younger women might be more affected emotionally than older women and men, according to the federal health-care research agency.

Westburg said it's been difficult adjusting to life with a failing heart.

"I don't work. I'm still not able to unload the dishwasher. I don't drive very often," she said. "So I went from total independence to having to be very dependent."

Faith and family keep her from getting depressed, she said. But she knows heart disease might shorten her life.

"I wrote my family letters and put them in the safe. I said goodbye to them."