You need to know that the inside of an airplane cabin is not like traveling in a car or train, the environment is a stressor to our bodies-especially the heart. The cabin air is  breathing air with 10% humidity at 5-8,000 feet above sea level.  So YES the air has less oxygen (‘is thinner’) for a healthy person this causes the heart rate to do more work.  DocHandal’s latest podcast on her iTunes channel explains vital need to know before you go information for anyone with a past or present heart issue.