Passive smoking, the inhalation of other people's tobacco smoke, is a fatal cause of heart disease, according to a new study by researchers at the University of California at San Francisco.

Stanton A. Glantz, a professor of medicine, and cardiologist William W. Parmley found that nonsmokers who live with smokers are about 30 percent more likely to die of heart disease than are nonsmokers who do not.

The risk in the workplace, they said, was potentially higher.

The researchers concluded that passive smoking is linked to about 37,000 deaths attributed to heart disease annually, as well as 16,000 cancer deaths. About 400,000 people die annually from tobacco smoking.

The UCSF report, prepared for the Environmental Protection Agency and published in the January issue of the American Heart Association journal Circulation, analyzes evidence from 11 human studies as well as laboratory research on biological effects.

The only human study that failed to show an increased risk was funded by the tobacco industry, Glantz said.

Much of the data was collected after 1986, when the Surgeon General and the National Academy of Sciences said that the link between passive smoking and heart disease was unclear and needed more study.

Glantz said the latest studies indicate that nonsmokers are more sensitive than smokers to cigarette smoke at very low doses. It can make platelets "stickier" and more likely to clot and increase plaque buildup on artery walls, both of which can contribute to heart attacks.

People who already have heart disease are potentially more vulnerable.

Tobacco Institute vice president Walker Merryman disputed the finding. "The evidence is exceedingly poor that environmental tobacco smoke is causally related to coronary heart disease," he said.