The great Greek physician Galen saw the heart as a furnace, imbuing the blood with "vital spirits." Eventually it became the province of Cupid, St. Valentine and love.

And now, St. Val's month of the heart has, not quite coincidentally, become the propaganda property of the American Heart Association.

Coyness aside, cardiovascular disease (CVD) is still the Number One killer in this country--in 1980 it accounted for more than a million deaths, about 51 percent of all deaths, says the American Heart Association. There are an estimated 42.3 million Americans with heart or blood vessel disease, so if it takes a preemption of Valentine's Day to call attention to all the ways we put ourselves at risk of literal heartbreak, nobody should quibble.

Americans are ever-so-slightly reducing the incidence of heart disease, and have been since the identification of dietary and behavioral risk factors, such as diets high in fats, sedentary life styles, highly charged emotional personalities.

Science has also learned that some risk factors are immutable--an inherited tendency to cardiovascular disease, for one. Yet even these can be minimized.

Dean Ornish, a young medical resident at Boston's Massachusetts General Hospital and a Harvard Medical Fellow, has now produced evidence that certain self-help techniques can not only help prevent the onset of heart disease, but actually reverse its course.

His study has just been published in the Journal of the American Medical Association and, considerably revised, adapted into a self-help book, Stress, Diet & Your Heart ($16.95, Holt, Rinehart and Winston).

Ornish is the first to admit that the link of stress to heart disease and, conversely, the link of meditation techniques to the lowering of blood pressure has already been demonstrated--by, for example, Dr. Herbert Benson and his "relaxation response." Furthermore, the Framingham Heart Study--the still ongoing epidemiological examination of about 5,000 people in the industrial suburb of Boston--and subsequent smaller studies have identified a definite link between diet and heart disease.

But his study, says Ornish, marks the first time "anyone has combined stress control and diet in a controlled study, looking at tests that measure the heart's function rather than risk factors such as blood pressure or cholesterol."

And, it seems, a combination of stress management and diet is more than twice as effective as using just one or the other. It is an example of synergy, where two plus two can equal five.

(Just as the combination of smoking, high blood pressure and high cholesterol in the same individual, produces a risk factor more than three times greater than the risk of any of the three in a single person.)

Ornish, a Texan, might have been a candidate for CVD himself, even before he got through college. He was in a pre-med organic chemistry course at Rice University with a professor who saw his mission in life as weeding out those unfit for medical school.

"I hated organic chemistry," says Ornish, "but I really wanted to go to medical school. I began to worry about remembering and, as you know, when you try to study, the more you worry, the more you forget, which makes you worry more . . . So I began to take a friend's Valium in hopes of calming down enough to be able to study to get into medical school.

"It was crazy, there I was at age 18 [he's 29 now] trying to get into med school so I can help people and having to take Valium. I thought, 'something is not right here.' "

About that time his sister, once a "super-charged A-type" introduced him to her "meditation and yoga" teacher and Ornish says, "I figured it couldn't hurt." Swami Satchinananda, the teacher, taught him a few meditative techniques and wooed him away from his "typical college student diet of hamburger by gourmet, for one that was more based on fresh fruit and grains and legumes and vegetables."

The result was, says Ornish, "that, sure enough, I no longer needed a Valium and though I never did grow to like organic chemistry, I did well enough to get into med school."

But that wasn't all. As a medical student (at Baylor University) he became involved with setting up a preventive medicine and health-education resources network for the American Medical Students' Association and was encouraged by Herbert Benson to do some research of his own. To his parents' chagrin, he says wryly, but with full cooperation of Baylor medical services, he took off after his second year to do his own study on a small group of patients referred to him by his professors and their colleagues.

He put the 10 patients (in 10 rooms donated by a Houston hotel) on regimens of low-fat, high-complex-carbohydrate diets and simple meditation and visualization exercises. To Ornish's astonishment, their heart disease began to recede. Although then it was unclear why.

Since that study (while Ornish was finishing medical school), new research has established "coronary artery spasm," and "platelet clumping" as the major mechanisms for heart disease. Either can block the blood flow to the heart. Moreover, both high-fat diets and stress have been implicated in triggering a chemical that can cause either or both of those conditions. Finally, a series of non-invasive tests permitted specialists to monitor heart functions and the progress of heart disease.

Ornish reasoned that stress management and a diet low in fats ought to reverse the disease process. As a full-fledged doctor, he set up a larger study in 1980. Results of the second study of 46 patients, confirming his earlier findings, are the basis for the JAMA article and his book.

Among other findings, 91 percent of the patients had a decrease in pain from angina. The Ornish program is designed as an adjunct to "pills and surgery," which are "lifesaving when used appropriately, but they don't do much about the underlying causes of the problem . . . What happens is that patients get a bypass, go home, think they're cured, continue to eat the same way, respond to stress the same way and the bypass grafts themselves clog up--at a rate of 6 to 10 percent a year . . ."

Ornish offers this cartoon as explanation: A group of doctors feverishly mopping up the floor around an overflowing sink, using all manner of expensive mops and brooms and brushes . . . but nobody reaching over to turn off the faucet.

"In many ways," he says, "that's what we do."

* The diet: Basically, Ornish has divided food into five groups, ranging from the highest in fat and cholesterol (heavy beef, pork, egg yolks) to those highest in fiber and complex carbohydrates and entirely devoid of fat and cholesterol (grains, fruits, vegetables, legumes). He does not necessarily suggest that people give up everything, only that they "move over one group on the spectrum," and, as they feel better, keep moving in that direction.

* Stress control. This, he emphasizes, does not mean giving up an exciting, competitive life and "spending life sitting under a tree." It is, he says, simply a manner of knowing how to handle the stress, rather than eliminating it.

"There's nothing really special about this diet," says Ornish, "It's the way most of the world eats, and there is nothing special about the stress reduction techniques--they've been around for centuries."

He likes to quote this putative exchange between Mark Twain and his doctor: "If I give up wine, women and song will I live longer?" Twain asked. "No," came the answer, "but it will seem longer."

It doesn't, says Dean Ornish, have to.