Left sided chest ache/tearing sensation when I suddenly run / speed walk, but not when ramped up like being on a treadmill. 2 neg nst 01/13. Ideas?

Chest wall pain. Exercise puts stress on more things then just the heart. Rapid change in exercise level doesn't give your tissue a chance to adapt. Thai is why athletes warm up. The ribcage is very complex with many moving parts. The muscles of the shoulder arm complex the ribs the muscles between the ribs the sternum, the diaphragm, the heart and lungs all interact. Listen to your body, warm up.