Heart disease is the No. 1 killer of women. A recent study suggests a new score could determine the health risks for millions of women.

Two years ago, Leslie Power had the surprise of her life.

"I couldn't believe I was actually having a heart attack," she said.

Power was only 45. She did not realize she was at such high risk. A new study shows she is not alone.

"We found in the new data that many women were at much higher risk than we anticipated," said Dr. Paul Ridker, of the Brigham and Women's Hospital.

Researchers studied blood samples stored in freezers from almost 20,000 women ages 45 and older. They looked for risk factors that led to heart attack and stroke more than 10 years later. The findings appear in the Journal of the American Medical Association.

"We created a new risk score -- something called the Reynolds Risk Score," Ridker said. "It turned out this does a much better job of predicting accurately a woman's true risk of having a heart attack or stroke over the next 10 years of her life."

The Reynolds Risk Score measures factors like smoking, age, diabetes, hypertension and cholesterol. It also includes family history of heart disease and a new measurement of C-Reactive Protein (CRP) in the blood. It is a sign of inflammation in the arteries.

"You can be a high risk patient if your CRP is elevated, even if your cholesterol levels are low," Ridner said.

Old risk assessment show 9 million American women are at medium risk for heart disease. The Reynolds Risk Score could reclassify more than half of those women into lower or high risk.

To lower her risk, Leslie quit smoking and exercises more. She does not think any woman should be caught by surprise.

"I think what women need to understand is that they are at risk for heart disease," she said.