Last night I decided to try out the cardio setting on the treadmill for kicks. The fast tempo was roughly the pace I run my 1600s at, so that was good...but I didn't expect the increase elevation as well. Towards the end of the second interval I started to feel a side stitch like pain directly over my heart, the first time I've ever felt anything like that before. I was a tad alarmed so I slowed down immediately and walked and the pain went away almost immediately. I did feel like I could breathe a bit more deeply once the pain was gone. I'm a former smoker of 13 years who quit last year...and I've always wondered how strong/weak my heart was. Blood pressure is 120/80.