It can also cause death.
Air pollution "is a significant issue. There's no question," said cardiologist Sumeet Mainigi of Einstein Medical Center. "The problem is, not only is it significant, but it's also completely under-recognized by patients and doctors."
About 10 years ago, the American Heart Association published guidelines on cardiovascular risk and air pollution. But they were not incorporated into standard literature or practice, according to Mainigi.
Now, however, more and more people have come to recognize that there is "rigorous evidence" of a link between the two, said Aruni Bhatnagar of the University of Louisville School of Medicine, author of Environmental Cardiology: Pollution and Heart Disease.
Data from metropolitan areas show that air-pollution spikes are followed by spikes in cardiac deaths.
And long-term studies have shown that areas with high levels of air pollution have higher rates of cardiac mortality and shorter life spans.
Researchers don't have enough data to show whether air pollution ranks with other major risk factors for heart disease - smoking, diabetes, high cholesterol and high blood pressure. But "it definitely makes all those worse," said Mainigi.
Meanwhile, studies showing elevated risks from air pollution continue to mount.
In a study published Wednesday in the European Heart Journal, researchers analyzed records of more than 150,000 patients who had survived heart attacks, and found that subsequent death rates rose with increased exposure to small particles in air pollution.
Another study, published last year in the Journal of the American Medical Association, found that exposure to various kinds of air pollution - carbon monoxide, nitrates, sulfites and particles - were associated with changes in an electrocardiogram that signal a heart injury.
The particles, especially a category known as "fine particulates," may be the most worrisome, because they can go deep into the lungs. There, they can enter the blood stream - the cardiovascular system.
Also, they often have harmful chemicals attached to them.
One effect is that blood vessels start to lose their ability to dilate, leaving the heart less able to adapt to the body's needs.
Long-term exposure can have more dramatic effects, including making blood cells "stickier" and prone to clotting.
Particles are emitted from sources including vehicle exhausts, smokestacks and fires. Not surprisingly, researchers also have found increased problems in heart patients who live near highways. One study showed that heart-attack survivors who live 328 feet or less from a major highway have a 27 percent higher risk of dying from any cause in a 10-year period than someone living at least 1,000 meters away.
Mainigi, Bhatnagar and other cardiologists tell their patients to avoid exercise outdoors when pollution levels rise, and to stay indoors when they are high. Even driving in heavy traffic poses a risk when levels are climbing.
When indoors, minimize exposure by not burning wood, incense or candles, all of which release particulates. Install a good filter on heating and air-conditioning systems.
Levels of particle pollution are higher in warmer months, when air is stagnant.
Forecasts for current particulate levels are available from a variety of sources, some of which offer mobile updates.
The Delaware Valley Regional Planning Commission posts a daily forecast for fine-particulate matter - labeled PM 2.5, for the size of the particles, in micrometers - at AirQualityPartnership.org. The city's Department of Public Health also posts a daily forecast, at phila.gov/aqi.
The U.S. Environmental Protection Agency has a free app, AIRNow, that maps current conditions and ranks them, from good to hazardous. The information is also on the website AIRNow.gov.
American Lung Association (lung.org), also has a free app, State of the Air.
Contact Sandy Bauers at 215-854-5147 or email@example.com, or follow on Twitter @sbauers. Read her blog, GreenSpace, at philly.com/greenspace.