30 y/o, healthy, have run 1 marathon, exercised regularly for many years. History of childhood asthma w/ no know cause. Unmedicated most of teenage and adult life except for very occasional use rescue inhaler over the past 3 years, sometimes related to exercise, but usually not (I think it's undetected food allergies that cause flare ups). Since 2005 have had 3 instances of several week periods where my heart felt like it was pounding very hard especially at night, and the need to use rescue inhaler was frequent and unrelated to exercise. I've had 3 ekgs and one stress test, all normal. I was beginning to think it was anxiety and had stopped worrying about it being a heart or lung issue, but another strange incident today has me worried again. I was running at the gym and felt great on a 6 miler. I tend to reach at least 90% of max heart rate at end of my run. As I began to slow my pace to a jog for cool down, I felt what appeared to be a typical cramp in my left side just below my breast. Then after a few seconds I felt the discomfort radiate up my chest and into my shoulder and left side of my neck. I immediately slowed to a slow walk and briefly felt dizzy and nauseated. Within a few seconds of walking the pain and dizziness completely subsided but I noticed my breathing was very restricted and my chest felt very tight. A few hours have passed and my heart rate is normal (58 bpm even after my rescue inhaler which will speed up heart rate) but my chest feels "fluttery" and I don't feel like I'm breathing quite at full capacity... Did I just overdo it at the end of my run? Can this be a normal response if didn't breathe right for the last few minutes? Do I need to go back to the doctor and if so what else should they do after the normal ekgs and stress test?