All that changed by the time Devany endured a major heart attack last fall. In the intervening years, evidence has piled high that brain disease somehow worsens heart disease.

Now his UNC-Chapel Hill heart doctors routinely ask Devany about his anti-depression medicine, visits to his psychiatrist and the exercises he does to calm down. They want to know everything he tries to keep the depression in check.

"It's a new development," said Devany, who is 75 and lives in Chapel Hill. "In 1997, no one was talking about it at all."

The growing interest in this medical mystery originates with a frightening fact: People with depression appear to be two times more likely to die from their heart troubles than others, studies show.

That increased risk poses the same level of danger for heart patients as cigarette smoking. Also, heart patients with depression who live with heart disease appear to suffer more intense symptoms day to day.

The trouble is, no one yet understands the link.

"It's a little hard to get a handle on," said Dr. Alan Hinderliter, a UNC cardiologist interested in the phenomenon. "Clearly there is a relationship. Why that relationship exists isn't exactly clear."

But scientists have theories. The most obvious one focuses on behavior.

Anyone who has suffered depression knows the disease, when uncontrolled, makes everyday tasks difficult. People in the midst of depression are less likely to take their prescribed medications, stick with heart-healthy diets or exercise to take care of themselves.

"Depression interferes with important lifestyle factors," said Lana Watkins, a Duke University psychologist.

"People are less likely to adhere to what physicians tell them to do."

But less obvious factors may contribute as well. On microscopic levels, researchers find significant differences in the circulatory systems of people afflicted with depression.

For instance, their blood platelets, the smallest type of blood cells produced in bone marrow, can become more sticky. That condition could contribute to unwelcome blood clotting, said Hinderliter, the UNC doctor.

Also, the inner lining of blood vessels in people with heart disease appears less healthy. Problems with that lining can contribute to arteriosclerosis, or clogging of the arteries. Some researchers think both of those abnormalities may be linked to greater overall inflammation in the circulatory system in people with depression.

Nervous system, too

On top of that, researchers find that people with depression also display abnormalities in their autonomic nervous system, the parts of the body that control involuntary acts such as seeing, breathing and blood circulation. Sometimes their hearts beat abnormally.

"We don't have a clear understanding of how depression leads to these more systematic problems," Hinderliter said.

All this suggests, of course, that the physical effects of depression are more complicated than once believed, and that treating depression may improve more than a person's mood.

"We need to figure out what factors are underlying depression," said Watkins, the Duke University psychologist. "And we need to find ways to treat those factors."

First, diagnosis

The first step is diagnosing depression. Physicians admit they don't have a perfect record on that front.

The best estimates say only one-third to one-half of major depressions get diagnosed in a given year, said Wayne Katon, a psychiatrist at the University of Washington's medical school in Seattle.

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