Smog's been a big story from the Olympic games in Beijing, and today researchers have new data about the impact of pollution on the heart.
Experts from the American College of Cardiology found evidence that exposure to ultra-fine particles can damage heart and blood vessels.
They say when pollutants are inhaled, a series of negative reactions occur, including some that activate molecules that can hurt the heart.
Other studies show on high pollution days there's a spike in hospital admissions for heart attack and chest pain. The elderly and patients already diagnosed with heart disease or diabetes may be especially vulnerable.