An angiogram is an invasive procedure, but will tell you if you have coronary disease or not. It does not mean, however, that if you have coronary disease that it is the culprit of how you are feeling. It seems a little strange to me that 15 minutes into cardio your heart rate was only 120 (either very light cardio or you are in excellent condition); I think I would consider a second noninvasive study, such as a myocardial perfusion test ("nuclear stress test"); would also consider a 24 hour Holter monitor to looks for abnormal heart rhythm. If those are negative, you may not warrant proceeding to angiogram; if you are a more aggressive person by nature and you are willing to accept higher risk, then an angiogram may be appropriate but I would discuss the risk to benefit ratio with a cardiologist. Hope this was helpful!
I had an episode about a year ago that sounds exactly like what you experienced and then once again last week. The time a year ago I ended up taking myself to the emergency room because the pain and pressure in my chest had become so bad that I could barely breathe. All my tests came back normal and the Dr. gave me a dose of Atavan which helped me calm down a bit and my chest relax. I was able to leave after a few hours with only a mildly sore chest. My wife seemed to think I might have suffered a panic attack because the symtoms are really similar, and I responded to the Atavan. I always thought you needed to be a really stressful person to get panic attacks, but they can happen to you with no warning. When I had the episode last week, I was able to recognize the symptoms and layed down for a while and focused on my breathing. That helped me a bit at work since I didn't want to take any 'downers' at the office. When I came home I took one of my wife's Atavan's and it helped out too.