If you have atrial fibrillation (AFib)-the most common type of arrhythmia, according to the American Heart Association (AHA)-you may have heard that exercise can trigger it. However, a new study suggests that moderate exercise might actually lower your risk of AFib. Walid Saliba, MD, associate director of the section of cardiac pacing and electrophysiology at Cleveland Clinic, is all in favor of getting physical: "Exercise can play a significant role in decreasing the mechanisms that precipitate or worsen AFib," he says. AFib occurs when the hearts internal electrical system goes haywire. Instead of telling the heart to contract and relax in a steady rhythm, the electrical impulses speed up and multiply. "The abnormal rhythm isnt dangerous in itself," Dr. Saliba explains. "But it can make you breathless, dizzy and tired, as well as cause chest pain."