What Causes Strain In The Chest And Breathing Difficulty While Walking Upstairs?

I am 62 year old female. I do not smoke or drink and never have. I exercise on elliptical machine five to six days a week, 60 minutes, covering on average, 5+ miles, burning approximately 575 calories. Additionally, I do a 50 minutes Pilates exercise four to five times per week and a 25 minutes abs exercises four to five times per week. Nonetheless I get winded walking up a flight of stairs. Also, I feel heart strain and tired if I hold my arms overhead for a short period od time (30 seconds). I have been examined by a cardiologist who has given me several tests, including a stress test. I ve also seen a pulmonologist.