The intensity of the pain would have been helpful. if the pain was stabbing, then it might have been related to heart issues. Angina pectoris is a condition in which the heart muscle is not supplied with oxygen enough. This condition can be caused by clogged coronary artery or coronary artery spasm or both. If only coronary artery spasm was present, then the heart might have not been damaged and some of the tests you mentioned would have been within normal limits. The problem is that if there is no damage, the ECG can register angina pectoris causing pain only at the exact time when it appears. Any previous damage would have been registered with certain laboratory tests (Lactate Dehidrogenase, Creatine Kinase-MB) and the Stress test. Since the latter showed normal results, you might consult with neurologist if the problem is neurologic affecting some of the nerves in that area.

I'm 34 and work out reagularly. Whenever I do a really hard bootcamp workout I'm start to have sharp stabbing in my chest, heart. It happens later that day, not while I'm working out. The pain is very intense and will last for 45 seconds or so and I can only take shallow breaths while I'm having the pain. This has been happening for years and I've been checked out with EKG and stress test and still found nothing. What could it be and is it safe for me to work out really hard, on a scale of 1 to 10 the workout is a 10.