Most of the knowledge about the prevention of heart disease today involves those all-important risk factors, and much of the research identifying them comes from an ongoing project known as the Framingham Heart Study. Since 1949, public health officials have followed the living habits, medical histories and deaths as they occurred of some 5 000 residents of this Boston suburb. Over the years they have found three major risk factors associated with heart disease: cigarette smoking, high blood pressure and high blood-cholesterol level. Other important risk factors identified include diabetes, lack of excise, stress and obesity, which puts additional strain on the heart.

What it all comes down to, according to Dr. William Castelli, the present director of the Framingham Heart Study, is that every fifth man in this country and every seventeenth woman gets a heart attack before the age of 60. "These are not old fogies dying of coronary heart disease," he says. These are young fogies, men in their forties and fifties. That is the American epidemic. And what we are saying is that if a doctor or anyone did a simple little adjustment of their risk factors, they could avoid falling prey to heart disease early in life.

The younger the heart patient, the more likely he is to exhibit one or more of the major risk factors, and the more risk factors present, the more the chance of heart attack multiply. But there are also several factors beyond our control that increase the risk for a heart attack. The risk is known to increase with age; four out of five deaths from heart attack occur after the age of 65. Heart attacks are also more likely to occur in men than, women, for reasons largely unknown, although women have about as much heart disease as men.

It also appears that a tendency toward heart disease is hereditary. "I think genetics plays a major role in heart disease," says Dr. Jan Breslow, a geneticist at Rockefeller University who has isolated and abnormal gene that appears to be responsible for an individual's inability to clear normal amounts of cholesterol from the blood. "But it's probably a combination of both environment and genetic susceptibility. You just can't tease the two parts."

Genetic defects may explain why some people on a reasonable diet, who exercise, do not smoke and are not overweight are struck down a heart attack by fiftieth birthday. Breslow estimated that about 5 to 10 percent of the population are probably highly resistant. Those who are highly resistant exhibit what Breslow calls the Winston Churchill syndrome. They are people who live to a ripe old age despite excess weight, a smoking habit and a tendency to drink.