I have to be careful with answering a question like that in a forum. At times someone could be asking that because they are fearful in general, and would be better served talking to a professional about anxiety. There are plenty of references about symptoms online although I don't suggest spending much time looking for that, because everyone's situation is different-all of it could be triggering. I've had two heart attacks. They are very survivable in many cases when you get professional help soon on onset.