I would like to know why my heart pounds really hard for hours after heavy exercise - not fast - just hard. I've asked doctors and searched on the internet, and the best I can tell - know one really knows. I'd really like to know what causes this and if it is an indication of a problem. Example - if I bike for about 30 miles, when I go to sleep that night, my heart will "pound" for hours, until about 3 am, and I usually can't sleep. I'm 59 years old and I believe in good shape - not great, but I think good shape. Am I exercising too hard? I first noticed this after biking the MS 150 in 1993 - my heart pounded for 2 days! I've asked my doctors and no one seems to have a good answer. I live at 6000 ft elevation. Last weekend, I hiked about 8 miles at 10,000 ft elevation, and after returning home I could not sleep all night - my heart pounded until about 3 am. Any advice will be appreciated. - Ben