Heart attacks may have long, slow causes, but they're still sudden events. Activities like a bout of exercise, doing cocaine, or getting really pissed off can set off a heart attack. Researchers in Germany looked at whether being in traffic could set off heart attacks, too.

What the researchers wanted to know: What is the relationship between being exposed to traffic and having a heart attack?

What they did: The researchers used a registry in Augsburg, southern Germany, that collects names of people who survive heart attacks. When people are added to the registry, a nurse asks them about what they did in the four days leading up to the heart attack—how much they slept, how long they spent outside, whether they experienced extreme anger or joy, and so on. They looked at things like whether people were more likely to have been exposed to traffic on the day of the heart attack than in the previous three days. Or, given that all these people had had heart attacks, the researchers looked at the chances that the heart attacks occurred soon after people were exposed to traffic.

What they found: Exposure to traffic increased the risk of having a heart attack in the next hour by 2.6 to 3.9 times. Most people were traveling in a car, but the researchers found that traveling by public transportation could lead to heart attacks, too.

What the study means to you: It's not as though these people were riding the bus, minding their own business, arteries as clean as a lamb's, and suddenly traffic struck them down; they were already at risk. This study says traffic might set off a heart attack, but that doesn't mean people with no risk factors will get into their cars and fall down dead. The authors say this study suggests that efforts to clean up city air could help people at risk for heart attacks.

Caveats: The study can't tell what it is about traffic that appeared to set off heart attacks—stress, noise, and pollution are all possibilities. The authors say that because public transportation seemed to have a similar effect, the stress of driving can't be the only reason. Particulate pollution in the air is more likely, they say.

Find out more: Find out how bad the traffic is in your city, using the Texas Transportation Institute's 2004 Mobility Study.

Check out the EPA's website to get information about the air quality where you live.

Read the article: Peters, A., et al. "Exposure to Traffic and the Onset of Myocardial Infarction." New England Journal of Medicine. Oct. 21, 2004, Vol. 351, No. 17, pp. 1721-1730.

Abstract online: http://content.nejm.org