The death rates for heart disease and stroke each dropped by about 30 percent between 1999 and 2006, allowing the American Heart Association to reach its 2010 goal of a 25 percent reduction in deaths four years early, researchers said last week.

“It’s one of the most remarkable achievements of modern medicine to have this kind of decline,” said Dr. Gregg C. Fonarow, a cardiologist at the University of California, Los Angeles’ Geffen School of Medicine who was not involved in the research. “But there is still obviously a lot of work to be done. We still have the number one and [number] three killers of men and women in the United States.”

But experts fear that the declines soon might be reversed. “Although death rates are declining, several of the risk factors leading to heart disease are increasing,” said Dr. Suzanne Steinbaum of Lenox Hill Hospital in New York, an American Heart Association spokeswoman. “There is an increase in obesity, diabetes and physical inactivity, which all lead to heart disease and stroke.”

The annual report, published online last week in Circulation: Journal of the American Heart Association by the Heart Association in cooperation with the Centers for Disease Control and Prevention and the National Institutes of Health, showed that death rates in the United States from heart disease and stroke each dropped about 5 percent from 2005 to 2006, the most recent year for which data are available.

Including the new data for 2006, researchers found a 30.7 percent reduction in heart disease deaths since 1999 and a 29.2 percent reduction in stroke deaths.

Those gains, Fonarow noted, were fueled by better preventive care for people in high-risk groups, more effective treatments in the hospital for those suffering heart attacks and strokes, and better care to prevent recurrences after a first episode.

Nonetheless, 829,072 Americans died of heart attack and stroke in 2006, 34.2 percent of the total or one in every 2.9 deaths. Nearly 2,400 Americans die of cardiovascular disease each day, an average of one death every 37 seconds.

Total cholesterol levels, a major risk factor for heart disease, decreased about 2 percent during the study period for men over 40 years old and women over 60, but remained steady for younger people, despite the growing use of cholesterol-lowering statins.

Obesity, another risk factor, is climbing. The percentage of children in the 95th percentile for obesity rose from 4 percent in 1971-74 to 17 percent in 2003-06, according to the report.

And despite widespread recommendations promoting exercise, 62 percent of adults reported no vigorous activity lasting longer than 10 minutes per session, the researchers said.