I have Mitral Valve Prolapse. My doctor put me on Tenormin to help me cope with the chest pain. On Tenormin I still get chest pain, but it is not as bad or as regular as before. Yesterday I went to the gym. I did cycling for 10 minutes and walking for 20 minutes. This is what happened: (My resting heart rate is 59) During the cycling, my heart rate went from 79 - 95, regular. While it was on 95, it suddenly jumped to 104, then to 79 and then back to 93.. It then continued normally. With the walking the same thing happened. I was on constant 96, then I decided to run just for 1 minute. My haert rate went to 104, then dropped to 83, jumped to 120 and then went back to 105. What is happening? I dont have pain when this happens, but I have a VERY uncomfortable feeling in my chest, I also feel VERY light headed and as if I was going to faint. I felt VERY tired afterwards... but not tired because of normal excersise... just VERY weak. Any idea what this could be? I am a female, 30 years old. Thanks, help will be appreciated :-)