so the intensity is the same on long or short runs.I run on a treadmill.
lots of family at very young age having heart attacks and such.
darn,I hope I do not have to give up running.
I would call your doctor and get in to see him/her and get checked out, just to make sure nothing is wrong. How fast are you running on your short runs? I find that sometimes I run faster on my shorter runs (30-40 minutes) than I do on my longer runs (40-70 minutes long), so the intensity and work load on my heart hard is greater.
Maybe that's the case for you, and it might be bringing on symptoms (palpitations, etc.)
Also, you're at an age at which maybe you could be in perimenopause. The hormone changes can bring about some heart symptoms (palpitations, arrthymias, etc.) in some women.
When you see the doctor, make sure you bring in your family history info (any biological parent, biological sibling, etc. have heart problems? If yes, at approximately what age?) and also a list of any and all over-the-counter stuff you may be taking (anti-inflammatories for running pains? vitamin pills, herbal medicines, etc.)
Good luck--and let us know what you find out!