However, a new report from the Institute of Medicine says smoke free laws don't hurt business but do prevent heart attacks.
Many people associate smoking with lung cancer, but doctors say about a third of all heart attacks in the U.S are related to smoking.
The report concludes that while heavier exposure to secondhand smoke is worse, there are no safe levels.
It also cited circumstantial evidence that even less than an hour's exposure might be enough to push someone already at the risk of a heart attack over the edge.
Researchers say it's difficult to say who is most at risk.
"A lot of people don't know if they have heart disease until they have their first heart attack, and so people are not aware if they're at risk. Therefore, the most prudent thing is reduce your exposure to secondhand smoke," said Dr. Lynn Goldman, Johns Hopkins University.
According to the government more than 126 million non-smoking Americans are regularly exposed to someone else's tobacco smoke.