 Nonsmokers are much more susceptible to heart damage from secondhand smoke than are smokers because their bodies haven't built up defenses against the onslaught of tobacco poisons, researchers say.

"The cardiovascular system adapts to insults," said Stanton Glantz, a professor of medicine at the University of California at San Francisco and an anti-smoking activist.

The conclusion is not new but was drawn from the most complete review to date of studies on how secondhand smoke affects the heart and blood vessels.

It also heightens the debate over secondhand smoke, indicating that even small amounts can endanger nonsmokers. The tobacco industry claims that the link between secondhand smoke and heart disease is unproven and that, in any case, non-smokers breathe in very little cigarette smoke.

"When you take a nonsmoker who doesn't have all this garbage in their body, and you put a little bit of it in, you get a big effect," Glantz said.

"Smokers are chronically poisoning themselves with cigarette smoke. ... The smoker's cardiovascular system has done what it can to adapt - adding a little more doesn't make much difference," he said.

Glantz and Dr. William Parmley, chief of cardiology at UCSF, pulled together data from more than 80 previous studies. Their review is published in today's issue of The Journal of the American Medical Association.

About 47,000 people a year die from heart disease caused by secondhand smoke, and 150,000 others suffer nonfatal heart attacks, according to an analysis prepared last year for the Occupational Safety and Health Administration. An estimated 3,000 people die of lung cancer annually because of secondhand smoke, OSHA said