CHICAGO -- Mammograms are designed to detect breast cancer, but new research shows mammograms may predict an illness that is an even bigger killer of women -- heart disease.

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Radiologists generally look for cancer, not heart disease, when they analyze mammograms. But a researcher said the X-ray readers can help women fight heart disease, too.

A Mayo Clinic study presented in December at a meeting of the Radiological Society in Chicago found that the X-ray images can spot calcium buildups in breast arteries. The researchers said the calcification can indicate a higher risk of developing heart disease.

Calcification or calcium deposits are as unmistakable to radiologists as abnormal breast arteries.

The study reviewed mammograms from 1,880 patients who underwent coronary angiography and mammography within one year of each other at the Mayo Clinic from 1991 to 2001.

Women in the study with significant breast artery calcifications were 20 percent more likely to have heart disease than women with none, even when there were no symptoms.

"The calcifications that develop in arteries are so typical that it's very, very rare to mistake them for calcifications that potentially might be harmful or represent a tiny cancer," Brigham and Women's Hospital Dr. Jack Meyer said.

Dr. Christopher Cannon, a cardiologist, calls the research an important first step.

"They don't have consequences if they're in the breast, but it's a screening tool that you can see them there, that might be a hint that there may be blockages in other arteries where it's more dangerous," Cannon said.

Given the fact that 365,000 women die of heart disease each year -- compared to about 40,000 from breast cancer -- doctors have begun debating whether mammograms should now be used to screen for heart disease.

Sixty-three percent of women who die suddenly from coronary heart disease will have no previous symptoms of the disease, according to the American Heart Association.

"We are looking in cardiology for noninvasive tests to screen for heart disease, which is such a problem. This is a test that's done in hundreds of millions of women, and so, it's potentially a way to save lives," Cannon said.

The American Heart Association calls the research preliminary, but says if it holds true, mammograms could offer an important piece of information in identifying women at risk of dying from the nation's No. 1 killer.

"The fact that so many women die each year unaware of their heart ailments illustrates the need for better detection of coronary heart disease," said co-author Dr. Dana Whaley, senior associate consultant in radiology at the Mayo Clinic. "Mammograms are already paid for in terms of time and health care dollars. This routine exam also may be a useful screening tool for coronary artery disease."