Coronary heart disease does not develop overnight, but nearly half of all heart attacks -- both fatal and nonfatal -- occur seemingly without warning. In the unsuspecting victims, the main warning signs of heart disease -- usually the chest pain known as angina -- go unnoticed until a significant portion of the heart is damaged beyond repair.

Research has shown that the distressed heart does send an alarm that shows up clearly on a routine electrocardiogram. And new studies are demonstrating the role that personality plays in determining who experiences silent myocardial ischemia and whether behavioral change can help reduce sudden heart attacks.

"We should be able to look for things in a person's natural environment that trigger ischemia, and use various behavioral and stress-management techniques to modify at least some of those things and reduce the odds of a person suffering a heart attack," said psychologist Kenneth E. Freedland, professor of psychology at Washington University School of Medicine in St. Louis.

Physicians have known about silent ischemia for years and have been able to detect it during routine stress tests. These tests are taxing enough to produce angina in people with severe atherosclerosis, the hardening of the arteries that causes a heart attack.

When angina occurs, the electrocardiogram shows an abnormal electrical signal. It turns out, though, that this same signal occurs even when patients do not report feeling angina. In fact, once physicians began looking for it, they found that silent ischemia occurred about four times more often than ischemia with angina. In addition, about 2.5 percent of adult men who took stress tests exhibited silent ischemia without experiencing angina at all, either during the test or before taking it.

Since no one knew what to make of these findings, they were generally dismissed as meaningless as far as diagnosing heart disease was concerned. That attitude changed in the early 1980s, when it became obvious that silent ischemia was not merely a laboratory curiosity. Two groups of cardiology researchers -- one led by Carl Pepine at the University of Florida, the other by Andrew P. Selwyn at Hammersmith Hospital in London -- used a portable electrocardiogram recorder called a Holter monitor to see if patients known to have heart disease displayed silent ischemia during normal daily activities.

"Sure enough, these patients had many more silent ischemic events than 'noisy' ones," said psychologist Nancy K. Norvell, who was a member of Pepine's team.

To find out which routine activities provoke silent ischemia, David S. Krantz, medical psychologist at the Uniformed Services University of the Health Sciences in Bethesda, and cardiologist Alan Rozanski of the UCLA School of Medicine asked patients fitted with a Holter monitor to keep a diary of their daily activities.

Researchers found that most episodes were not provoked by strenuous activity.

"Most events occurred while people were involved in routine mental activities -- reading the newspaper, deciding what to have for breakfast and so on," Kranz said. But such events occur only to people with heart disease.

Researchers also found that most ischemic events occurred in the morning; the number dwindled as the day progressed. "It seems as if the act of waking up and engaging in normal morning activities is enough to trigger ischemia," Krantz said.

Rozanski and Krantz explored the role stress plays in inducing silent ischemia. Volunteers performed three mentally stressful exercises, one non-stressful mental activity and an exercise stress test. The results were surprising: Mental stress was just as likely to cause silent ischemia in the coronary patients as was exercise testing.

"Since mental stress may occur more frequently than stress from exercise in daily life, it could represent an important and largely unrecognized factor in the precipitation of more severe clinical coronary events," they wrote in an article published in 1988 in the Journal of the American Medical Association.

The other important result from the study by Rozanski and Krantz was that silent ischemia induced by mental stress occurred at only slightly elevated heart rates -- the same link observed in earlier Holter monitor studies. In contrast, exercise-induced ischemia, whether painful or silent, occurs only when the heart beats much faster than normal.

To appreciate the significance of this finding, it is important to understand what triggers ischemia. The heart, like any other muscle, needs an adequate supply of oxygen to work. If its demand for oxygen rises, then so must its supply. When the supply is not equal to the demand, ischemia results. In a healthy circulatory system, the arteries nourishing the heart are pliable. They dilate, or expand, when the heart's oxygen demand increases -- while exercising, for example.

In contrast, coronary arteries affected by severe atherosclerosis are stiff and, when demand increases, the arteries cannot dilate and increase the supply of blood. The heart cannot get enough oxygen; muscle spasms result and ischemia occurs.

But as Pepine and Selwyn each noted in their daily-life studies, and as Rozanski and Krantz found in their mental-stress tests, the majority of ischemic events occur when the heart beats only slightly faster than normal. As Krantz explains, the solution to this apparent quandary lies in the supply and demand equation. "Ischemia is a matter of an imbalance . . . In exercise-induced ischemia, the demand is very high. But in stress-induced ischemia, the demand is not very high, so the supply must actually be decreasing under stress."

In other words, stress must somehow be causing the hardened coronary arteries to constrict instead of dilate. These results were intriguing because they suggested that there is a direct link between stress and physiological changes in coronary arteries.

To test this hypothesis, Selwyn's group measured the diameter of the left anterior descending artery -- the major blood supply to the heart's pumping chamber -- while subjects performed a mental-stress test.

The result, Selwyn said, showed that coronary arteries obstructed by atherosclerosis responded abnormally during mental stress. "Healthy arteries dilate during stress, but atherosclerotic arteries actually dilated much less or even constricted during the stress tests," he noted.

Other researchers are trying to distinguish those patients who experience angina from those in whom ischemia remains silent. One factor may be that patients who do not report angina while experiencing silent ischemia seem to be less reactive to stress.

Psychologist Holly Hills, working with Norvell and Pepine, measured changes in heart function during a mental-stress test in individuals with significant coronary-artery disease who experience only silent ischemia, and a control group of healthy subjects. The volunteers answered questions designed to assess stress perception, hostility and symptom reporting.

Researchers found that the healthy subjects had a more pronounced physical reaction -- larger increases in blood pressure and heart rate -- to mental stress than did the silent ischemia group. But in addition, says Norvell, "our asymptomatic patients were much less neurotic and much less aware of their autonomic activity -- their heart beating, for example -- than the healthy with no documented coronary-artery disease.

"Perhaps," she said, "this flattened reactivity to stress actually protects these patients from having even more ischemic events. It may even be that people who have predominantly silent ischemia are normal, while those with angina have a faulty mechanism for dealing with stress."

Researchers at Duke University have launched a four-year study to see whether exercise or stress-management techniques can help cardiac patients reduce the frequency and duration of ischemia.

Patients will be taught to become more aware of stress and to modify their response to stresses they cannot change.

If stress management or exercise therapy helps cardiac patients, the key problem will then be to identify people who have silent ischemia and are unaware of it. "We certainly cannot start doing stress tests on the population at large," said Freedland, "so we would like to develop a psychological profile that physicians can use to identify patients who may appear asymptomatic but actually have severe coronary-artery disease."

Joseph Alper is a freelance writer in St. Paul, Minn.