Trouble on treadmill

I am a 34 year old female with an arrhythmia(when bad, over 10,000 PVC's per day,) and a dilated heart.  My doctor isn't too concerned about the dilated heart, but I am beginning to be.  The past three times  that I have exercised on the treadmill I have gotten chest tightness and difficulty breathing.  Today while on the treadmill I experienced the same symtpoms and my heart rate shot up to 200 very quickly and I felt like I was going to pass out.  I didn't feel well for about an hour, then later on in the evening I felt PVC;s.  The only thing different about my workout the past three days is that I increased the incline.   Normally  don't feel this way while exercising.  I am not obese, I need to lose 20 lbs, but can't figure out what the problem is. Should I be concerned?