(MNN) -- People with heart problems are advised to watch what they eat and avoid stress during the holidays.  But another concern that's often overlooked is air quality.  Mayo Clinic cardiologist Dr. Sharrone Hayes says make sure before you start firing up that fireplace that it's clean-burning and you're not going to be causing extra particulate matter in your home.  Dr. Hayes cautions that air pollution can cause breathing problems and strain the heart, a risky situation for people with cardiac concerns.