Although I have heard rare cases of excersize-induced heart attack, usually there are other facters invovled. Most docs will tell you that good excersize that raises the heart rate actually makes your heart stronger (remember, it is largely made up of muscle) and makes it less likely for people without other risk factors to have a heart attack in the future. Talk to your pdoc about this... it sounds like some form of panic disorder, but I am no expert. Hope it gets better!