Speeding Heart during exercise

[Maroc1]

I am a 29 year old female.  Since my early twenties, I have had problems with my heart speeding up very rapidly during exercise.  For example, when I am at the gym, the machines that have heart rate monitors are unable to track my heart rate after only a few minutes.  While on the machine, I will watch my heart rate surge from normal to above the recommended rate in one or two minutes and then after that, the machines cannot register my heart rate at all.  Also, when I manually monitor my heart rate (taking a pulse count with my fingers)  I am always way above the recommended rate within only a few minutes.  Another symptom I have is that I am extremely tired for about two days after one thirty-minute work out. I have mentioned this to my doctor, but he didn't seem concerned...and didn't really ask me any more questions.  Should I be concerned?  What could be causing this?

[mabebesc]

I have found the same thing with me .  All my life, when I took aerobics classes or exercised, my heart rate always went up fairly high.  When we had to take our pulses, mine was always the fastest from all my friends.  I never gave much thought about it .  I figured it was because I was out of shape. I don't quite know why you are so tired for a couple of days afterwards. Do you only feel tired after exercising? If this continues to concern you, I would check back with your DR, again.
Betty

[Momto3]

Awhile back, when I was on the treadmill (stress test), I noticed that my HR jumped up FAST!  I asked the doctor and was told it was most likely due to deconditioning.  Have you been working out for awhile, or is this a new routine for you?  

To what does your doctor attribute the quick-rising HR and fatigue?