Although it was once believed that women were immune to heart disease, this notion has been disproven, and to a certain extent, displaced. But the fact that women generally develop heart disease later in life has led to another dangerous myth: that younger women don’t get heart disease.

On the contrary, it’s been known for years that young women, but not older women, have twice the risk of dying after heart attack than men of similar age.

A study by researchers at the Yale School of Medicine, published in JAMA Network Open, looked at heart attacks in 2,264 patients ages 55 or younger, and found some surprises.

The key finding is that young men and women often have different risk factors. Seven risk factors — diabetes, depression, hypertension (high blood pressure), current smoking, family history of heart attack, low household income, and high cholesterol — were associated with a greater risk of heart attack in women. The highest association was diabetes, followed by current smoking, depression, hypertension, low household income, and family history.

Among men, current smoking and family history of heart attack were the leading risk factors.

“This study speaks to the importance of studying young women suffering heart attacks, a group that has largely been neglected in many studies and yet is about as large as the number of young women diagnosed with breast cancer,” says Harlan M. Krumholz, M.D., the Harold H. Hines Jr. Professor of Medicine at Yale, and a pioneer in the study of heart disease.

The study shows the urgent need for more awareness among younger women and their physicians.