Jean G. Miele's heart attack happened on a sidewalk in Midtown Manhattan last May. He was walking back to work along Third Avenue with two colleagues after a several-hundred-dollar sushi lunch. There was the distant rumble of heartburn, the ominous tingle of perspiration. Then Mr. Miele, an architect, collapsed onto a concrete planter in a cold sweat.

Will L. Wilson's heart attack came four days earlier in the bedroom of his brownstone in Bedford-Stuyvesant in Brooklyn. He had been regaling his fiancée with the details of an all-you-can-eat dinner he was beginning to regret. Mr. Wilson, a Consolidated Edison office worker, was feeling a little bloated. He flopped onto the bed. Then came a searing sensation, like a hot iron deep inside his chest.

Ewa Rynczak Gora's first signs of trouble came in her rented room in the noisy shadow of the Brooklyn-Queens Expressway. It was the Fourth of July. Ms. Gora, a Polish-born housekeeper, was playing bridge. Suddenly she was sweating, stifling an urge to vomit. She told her husband not to call an ambulance; it would cost too much. Instead, she tried a home remedy: salt water, a double dose of hypertension pills and a glass of vodka.

Architect, utility worker, maid: heart attack is the great leveler, and in those first fearful moments, three New Yorkers with little in common faced a single, common threat. But in the months that followed, their experiences diverged. Social class - that elusive combination of income, education, occupation and wealth - played a powerful role in Mr. Miele's, Mr. Wilson's and Ms. Gora's struggles to recover.

Class informed everything from the circumstances of their heart attacks to the emergency care each received, the households they returned to and the jobs they hoped to resume. It shaped their understanding of their illness, the support they got from their families, their relationships with their doctors. It helped define their ability to change their lives and shaped their odds of getting better.

Class is a potent force in health and longevity in the United States. The more education and income people have, the less likely they are to have and die of heart disease, strokes, diabetes and many types of cancer. Upper-middle-class Americans live longer and in better health than middle-class Americans, who live longer and better than those at the bottom. And the gaps are widening, say people who have researched social factors in health.

As advances in medicine and disease prevention have increased life expectancy in the United States, the benefits have disproportionately gone to people with education, money, good jobs and connections. They are almost invariably in the best position to learn new information early, modify their behavior, take advantage of the latest treatments and have the cost covered by insurance.

Many risk factors for chronic diseases are now more common among the less educated than the better educated. Smoking has dropped sharply among the better educated, but not among the less. Physical inactivity is more than twice as common among high school dropouts as among college graduates. Lower-income women are more likely than other women to be overweight, though the pattern among men may be the opposite.

There may also be subtler differences. Some researchers now believe that the stress involved in so-called high-demand, low-control jobs further down the occupational scale is more harmful than the stress of professional jobs that come with greater autonomy and control. Others are studying the health impact of job insecurity, lack of support on the job, and employment that makes it difficult to balance work and family obligations.

Then there is the issue of social networks and support, the differences in the knowledge, time and attention that a person's family and friends are in a position to offer. What is the effect of social isolation? Neighborhood differences have also been studied: How stressful is a neighborhood? Are there safe places to exercise? What are the health effects of discrimination?