In the last 2 days, I have experienced a shortness of breathe and tightness from shoulder to shoulder while taking a short walk. In both cases he symptoms go away in minutes, after stopping my walk. No issues follow. A week ago i walked 14,000 steps in 6 hrs without similar symptoms. I had stent put in 18 months ago, and saw my heart dr 2 months ago. I had a knee replaced 6 months ago and have been working out, no walking to speak of, pedaling and lifting. 2 years ago I had shortness and dizziness attributed to a lung virus.