For Dr. Dean Ornish's cardiovascular patients, "open heart" doesn't mean bypass surgery. His is a spiritual sort of open heart -- as in "open your heart" -- and his patients are treated, by and large, in group support sessions, rather than on the operating table.

Nevertheless, there is emerging evidence that Ornish, with his noninvasive techniques, is accomplishing the same ends as are his scalpel-wielding colleagues. And although it is too soon to make absolute claims, Ornish personally believes that his way may be longer-lasting.

Ornish, author of the 1983 book "Stress, Diet and Your Heart," is a proponent of the now widely accepted view that diet and exercise are effective ways to reduce the risk of heart disease, especially when they are combined with still relatively unconventional mind techniques as yoga, meditation and visualization.

Now the maverick physician is testing his hypothesis that established heart disease can actually be reversed using these techniques. It is a thesis most heart experts view with skepticism.

Heart disease kills about half a million Americans every year. Heart attacks often occur when the arteries carrying blood and oxygen to the heart muscle are clogged with fat and cholesterol (plaque), restricted by blood clots or spasms.

Standard treatments include angioplasty, to force open the arteries; drug treatment, to thin blood and lower cholesterol; and bypass surgery, providing new routes for the blood.

As a medical student at Baylor College of Medicine in Houston, Ornish was struck by the number of people who, after having one bypass operation, had to have another. After the initial operation, people would "go home and do the things that made them sick the first time, so the new arteries became clogged as well."

He began preliminary studies on behavioral ways to approach heart disease and published early results in the Journal of the American Medical Association.

He showed in two small, short trials in 1978 and 1980 that "it appears to be possible to see remarkable improvements in just three to four weeks" when patients were taken off cigarettes and put on nearly fat-free diets and exercise regimens and taught basic relaxation and meditation skills.

"We showed that blood flow to the heart could be improved, the ability of the heart to pump blood improved and the contractility of the ventricle improved.

"Many people who had been out of work for years, incapacitated by chest pain, were essentially pain-free after just three or four weeks and able to go back to work full time."

But the two short studies and the 1983 book did not fulfill his dream: a more "definitive investigation of whether heart disease can be reversed by changing life style." The early work implied that it can, but it didn't look at "the underlying coronary artery blockages" to see if arteries were actually being cleared. In other words, people felt better using Ornish's regimen, but it's not certain their hearts were actually healthier. That is what Ornish is investigating today, with interim results due in the spring.

Now assistant professor of medicine at the University of California at San Francisco, Ornish has recruited all but a few of the 50 subjects his study will require. Each participant suffers from advanced cardiovascular disease; some have had angioplasty; some are surgery candidates; some cannot be operated on. (There are about 200,000 bypass surgeries every year in this country.) The study is being done at UCSF in collaboration with Pacific Presbyterian Medical Center in San Francisco and the University of Texas Medical School in Houston. It is being funded exclusively through private and corporate grants. For example, Continental Airlines flies participants to Houston for certain coronary scans unavailable at the San Francisco centers.

Of the 50 volunteers, 25 will enter Ornish's program and 25 will remain under the care of their cardiologists.

Because of the strict requirements for entrance, including a computerized angiogram that precisely measures and locates coronary blockages, the year-long study has been done on only small groups at a time. Studies of the first 18 have just been completed. Although Ornish is careful to avoid discussing precise figures that might prejudice his chances for medical journal publication, he spoke recently to a group of psychiatrists in the Washington area and described encouraging preliminary results, including significant reductions in blood cholesterol without the use of drugs.

None of the components of the Ornish program is especially new, but the method of administration and the rigorous standards to which the participants are held plus the high-tech testing, should, Ornish hopes, provide a more definitive answer to whether life-style changes can reduce the amount of plaque in a coronary artery, the blood cholesterol levels and the spasticity of the arteries, all of which contribute to heart attacks.

"There is a tremendous amount of interest in the public in this area," he said, "but on the one hand you have people who say of course you can reverse heart disease, go ahead and build centers even though there really isn't the evidence to support it.

"On the other, you have most cardiologists, who say that heart disease is impossible to reverse.

"And in the middle you have the general public, which tends to be rather confused by these conflicting claims."

Because studies, especially in animals, suggest that stress plays a role in clogging arteries and relaxation can help prevent blockages, if not reverse them, behavioral techniques are a major part of Ornish's approach.

Wherever he goes -- on fund-raising expeditions, for example -- Ornish likes to cite a 1980 study of rabbits. The study found that rabbits that were fondled and played with by lab assistants had 60 percent fewer blockages in their arteries than rabbits that were ignored, even though both sets of animals were fed the same high-fat, high-cholesterol diet.

A recent study in North Carolina showed that monkeys in stressful environments developed more blocked arteries even though they were fed the same low-fat, low-cholesterol diet as were their lab mates.

To introduce participants to the program, Ornish packs them and, sometimes, their spouses off to a resort hotel near Berkeley, Calif., for a nine-day orientation; to the diet (including cooking lessons, although the meals can be obtained in specially prepared portions that the program provides); to each other, in the all-important mutual support sessions; to the aerobic exercises and meditative and visualization techniques to mobilize the body's own healing capabilities.

There are no additional drugs, no shortcuts, no deviations, no exceptions, no cheating. "This is a scientific study," Ornish tells them, "and for it to be accurate, you have follow the program 100 percent." Ornish is 34. Most of the participants are over 50. They do what he says.

"They get to know each other really well," he told a group of psychiatrists and psychologists at the Medical Illness Counseling Center in Bethesda on a recent visit, "and what I'm really struck by is the similarity in how they view the world. They come from such diverse backgrounds -- we have people who are millionaires and we have people who can't afford to buy their pills; people with PhDs, people who dropped out of school in the third grade, people of all sexual preferences, races, religions, and yet they tend to view the world in strikingly similar ways."

In this study, and in his previous work, Ornish has found that many heart patients have a world view "that goes something like this:

" 'I really feel isolated from the world and cut off and alone . . . If only I had -- whatever it is, power, sex, beauty, money, success, love -- then I'd be happy, then I'd be content; then I'd feel good about myself.'

"Once people set up that view of the world, no matter how it turns out, they end up feeling stressed. If they don't get whatever it is they feel they need, they feel stressed; if somebody else gets it they feel even more stressed and it reinforces their view of the world. And even if they do get it, it is good for about 10 or 15 minutes. All that reinforces the misperception that their happiness came from getting it, and whatever it is is never enough.

"It is a cycle, a treadmill that these people have been running on forever . . .

"We try to show them this way of looking at the world is itself disease-causing. We have an unusual number of people who are uncomfortable with who they are, and they create this image of who they want other people to think they are as a way of getting the love and respect they crave.

"We have a man who pretended to be an Olympic athlete who wasn't. We didn't find it out until after he died.

"We have others who are in fact quite different from how they portray themselves.

"With these people, no matter how it turns out, they lose. If they don't get the love and respect they want by creating this image they lose, and even if they get it they can't enjoy it because it's not real.

"And there is this chronic vigilance that goes with maintaining the image, reinforcing that sense of isolation. It can become lethal.

"So," says Ornish, "anything that increases a sense of intimacy in breaking down the barriers between us is healing in a literal sense of the word."

Meditation, for example, helps people experience the "inner peace" they believe money, love or success would provide. When they realize that contentment can be achieved without reaching their goals right away, stress levels are reduced.

After the initial nine days, patients are on their own, except for long meetings twice a week at which they eat together, exercise, meditate, discuss their problems and progress. They begin to heal themselves, Ornish believes.

The entire study will cost about $2.5 million, all but about $700,000 of which Ornish has raised. The protocol was at first shunned by traditional funding sources as "unfeasible," Ornish says. Critics said it wouldn't work, that nobody would adhere to his rigid standards and that surgery and drugs are more cost-effective. Ornish is hoping that when his interim data are published, those criticisms will be dispelled.