Sudden chest pain is the hallmark symptom of a heart attack. But a large new study shows that many people who are taken to hospitals for heart attacks never have chest pain and, as a result, are less likely to be treated aggressively. The consequences may be especially deadly for younger and middle-aged women. In a new study of 1.1 million people, a surprising 42 percent of women admitted to hospitals for heart attack never had chest pain. By comparison, just 30.7 percent of men who were admitted didn’t experience chest pain. Women were also more likely to die after a heart attack; the mortality rate for women in the study was nearly 15 percent, compared with 10 percent for men. “We think part of the reason is that women who are presenting with a heart attack might not have that classical presentation,” said Dr. John G. Canto, director of the chest pain center at Lakeland Regional Medical Center in Florida and an author of the study, which was published in The Journal of the American Medical Association. “So they may not be recognized as having a heart attack, and possibly some of these patients may present too late to receive lifesaving procedures.” Heart disease is the leading cause of death among men and women, not just in the United States but around the world, killing about seven million people a year. Until the 1980s, heart disease was largely considered a male problem, and many studies that focused only on men drew a narrow picture of the typical signs of heart attack: chest pain, shortness of breath and radiating pain in the neck, back, jaw and arms. But more inclusive research since then has shown that while female heart patients may exhibit these symptoms, they are also more likely to show symptoms that are less typically associated with heart attacks, like sleep disturbances and severe unexplained fatigue in the days and weeks prior, as well as cold sweats, weakness and dizziness during the attack. In their new study, Dr. Canto and his colleagues used data from a national registry of people admitted to hospitals for heart attack from 1994 to 2006 to look at differences in symptoms and mortality rates among men and women. The analysis, covering 1,143,513 people, showed that chest pain is in fact the most frequent symptom of a heart attack in both men and women. But a sizable minority of patients, about 35 percent over all, never had chest pain. Women under 55 who had heart attacks but no chest discomfort had two to three times the risk of dying in the hospital compared with men of the same age with classic heart attack symptoms. But “the difference markedly declined and nearly disappeared with increasing age,” said Dr. Canto, who is also the director of cardiovascular prevention research and education at the Watson Clinic in Lakeland. No one knows precisely why heart attack symptoms differ between men and women, but Dr. Canto speculated that many factors may be involved, including hormones. Many women who take birth control pills, for example, tend to have “stickier” blood vessels and arteries than men, he said. “We also know that in women, especially young women who have heart attacks, the mechanism of blood clot formation in the heart artery may be different than in young men,” he said. “They tend to involve more plaque erosion and sloughing off rather than the plaque rupturing, which is the classic way that heart attacks occur.” Those who are having a heart attack but do not feel tightness or pain in the chest may not realize what is happening, Dr. Canto said, and when they do show up for treatment, doctors may not immediately consider the possibility of a heart attack, particularly in women. As a result, the odds of immediately undergoing bypass surgery, heart catheterizations and other lifesaving procedures are decreased. The reality is that many doctors tend not to think that younger women have heart attacks, said Dr. Mario Garcia, a member of the American Heart Association and chief of cardiology at the Montefiore Einstein Center for Heart and Vascular Care in New York. But it’s also known from other studies that even women who do experience classic symptoms of a heart attack, including chest pain, are less likely to seek medical attention than men. “Men are quick to rush to see a physician,” said Dr. Garcia, who was not involved in the study. “Women worry more about their husbands than themselves.”