One simple question — Do you have trouble breathing? — may reveal as much about someone's risk of dying as the most relied-upon sign, chest pain.

Even people without any other cardiac symptoms were up to four times more likely to die of heart problems in the next few years if they had shortness of breath, a study of nearly 18,000 people suggests.

"Shortness of breath is not a sign to be ignored. It means make sure that your doctor knows about your symptoms," said Dr. Daniel S. Berman, senior author of the study, done at Cedars-Sinai Medical Center in Los Angeles.

Doctors take into account a number of risk factors and symptoms but especially chest pain when deciding whether someone might have heart disease and needs further tests. But it wasn't always clear how much weight they should give shortness of breath, Berman said.

Researchers reviewed the medical records for 17,991 patients who had stress tests to see if troubled breathing was useful in predicting someone's outcome. They found that the patients who reported being short of breath had a higher rate of death from heart trouble or any other cause.

"We don't know why some people get chest discomfort and others get shortness of breath. But in many patients we think the shortness of breath should be thought of as being an equivalent to having chest discomfort with exertion," Berman said.

Breathing problems have a number of causes, including lung diseases and heart damage or just being out of shape. It is the unexplained shortness of breath that might be a sign of heart disease, Berman said.

The findings were reported in Thursday's New England Journal of Medicine. The research was funded by Bristol-Myers Squibb Medical Imaging and Fujisawa Healthcare, which make products used in stress tests. Some of the researchers have received lecture fees or grants from the two companies.

Dr. Gerald Fletcher, a cardiologist at the Mayo Clinic in Jacksonville, Fla., and a spokesman for the American Heart Association, said women may benefit more from closer attention to shortness of breath since they are less likely than men to suffer classic chest pain.

"We need to be very careful that we don't neglect to identify symptoms in women because women have just as much heart disease as men," Fletcher said.

The study participants were sent to Cedars-Sinai for a sophisticated stress test over a 10-year period. They were asked if they had shortness of breath.

In the next one to five years, those with shortness of breath and no history of heart disease had four times the risk of death from heart problems than those without any symptoms (2 percent versus 0.5 percent per year) and twice the risk of those with typical chest pain (2 percent versus 1 percent).

Another researcher, Dr. Alan Rozanski of St. Luke's-Roosevelt Hospital in New York, noted that the study was done in a mostly white, middle- to upper-class population and the results may not be found in other groups. He said doctors are also increasingly looking at other symptoms such as fatigue, lack of sleep and depression.

"This is a disease that can masquerade and present in many funny ways," he said.