Hi. I was told by a friend of mine who had a stent put in recently and is attending a cardio rehab class at her hospital something I had never heard of before. The instructor told the class in a session recently that people with heart conditions should not do heavy aerobic exercise when the temperature dips below 40 degrees Fahrenheit because it makes the heart work harder and therefore should be avoided. I had never heard that one before. I have atrial fib but am doing well on the meds. I am used to doing walking sessions of about an hour. Well, the temperature is below 40 much of the time and I cannot always wait for it to get warmer. Isn t making sure that one is properly dressed for the cold adequate?? Thanks.