The study is the latest attempt to explain a decline in heart disease death rates that began in the 1970s. It's the first to gauge the effect of such powerful new treatment methods as cholesterol-lowering drugs and angioplasty, which allows doctors to open clogged arteries from within by inflating a small balloon.

"This is the first time anyone has looked at the big picture," says Sharonne Hayes, director of the Mayo Clinic's Women's Heart Clinic, who was not involved in the study.

Heart disease remains the leading cause of death in the USA, killing about a million people a year. But over the past two decades, death rates have dropped from 543 per 100,000 to 267 per 100,000 among men and from 263 per 100,000 to 134 per 100,000 for women.

In 2000 alone, researchers say, an estimated 341,745 people lived who otherwise might have died.

The researchers reviewed multiple studies that examined the effectiveness of heart disease treatments between 1980 and 2000. They matched that data with information on heart disease risks and deaths.

They found that even the newest and most potent treatments proved no more powerful than prevention. Treatment accounted for just 45 percent of the deaths that were averted, says study co-author Darwin Labarthe of the Centers for Disease Control and Prevention.

Labarthe also noted that obesity and diabetes have begun chiseling away at the recent gains. "You could say without exaggeration that this is a warning signal. We're already seeing an increase in heart deaths from obesity and diabetes."

The study, which is published in the most recent issue of the New England Journal of Medicine, also found:

- About 21,570 deaths were averted in 2000 by better treatment for heart attacks, including aspirin (7,735), clot-busters (2,410), bypass surgery (1,925) and angioplasty (1,070).

- Preventing second heart attacks saved 28,565 lives.

- Heart failure drugs prevented 30,235 deaths.

In 2000, aspirin helped save about 23,000 lives of patients with a range of heart conditions, compared with 9,000 for statins.

"It shows," Hayes says, "that some things that are low-tech and not particularly sexy, like taking aspirin, stopping smoking and walking, have the biggest impact on people's health."