Vienna, Austria ? An irregular heart beat is more common among men but much more hazardous when it occurs in women, according to the first major study to examine gender differences in the ailment.

The study presented Monday found that women who have atrial fibrillation were more than four times more likely to suffer a stroke than were men with the disorder.

The findings by scientists at Bispebjerg University Hospital in Copenhagen, Denmark, were presented Monday at the annual meeting of the European Society of Cardiology in Vienna.

Atrial fibrillation is the most common type of heart rhythm abnormality. It is estimated to affect up to 2 percent of all people, and up to 14 percent of the elderly.

Symptoms include palpitations, breathlessness and tiredness; the major hazard is an increased risk of stroke. It is about three times more common among men than women.

Nearly 5.7 million Europeans are estimated to have atrial fibrillation, a condition in which the two small upper chambers of the heart quiver instead of beating properly. In the United States, about 2 million people have it.

“This (study) raises awareness of the impact of cardiovascular disease among women,” said Dr. Sidney Smith, a professor of cardiology at the University of North Carolina at Chapel Hill and former president of the American Heart Assn. “It’s one more example that women are not protected from cardiovascular disease. We should do everything we can to dispel that myth that if you’re a woman you don’t need to worry.”

Smith, who was not connected with the research, noted that doctors had long believed that women were less vulnerable to heart disease than men, but that evidence is accumulating that they may not be.

The study involved 29,310 Danes over age 40 who had never had a stroke. They were followed for about five years.

Among them, 166 men and 110 women had atrial fibrillation.

There were 635 strokes, with 35 of them occurring in people with the irregular heart beat.