Cocaine--the drug that famously makes you feel like doing more cocaine--has a well-publicized history of causing heart attacks in users. But is the drug's threat to the nation's hearts more than, say, the air you've spent your entire life breathing?

According to a new study published in the Lancet, the answer is no. Granted, a cocaine user is still 23 times more likely to suffer a heart attack than a non-user, but researcher say the drug is the "final straw" cause in less than one percent of all heart attacks. Traffic emissions, on the other hand, trigger 7.4 percent of attacks, while "small air pollutant particles" are blamed for 4.8 percent.

Why does this matter? One word: exposure. As The Guardian's report on the study notes, "far more people are exposed to traffic fumes and factory emissions than cocaine," making smog a "far more important population-wide threat" than cocaine.

So enjoy that first lungful of city air when you leave work tonight. There's a 7.4 percent chance it could cause your next heart attack.