The EKG is essentially normal, although somewhat unusual for your age (more typical of a younger person). Why was it done?
I see you are offline, so let me add some comments for you to read when you return.
The "Borderline" may have been from the computer interpretation, and accepted by the overreading cardiologist because that's easier than taking the time to make the change to "Normal." It could have been b/o the somewhat slow heartrate, falling outside of the supposed "Normal Range" of 60-100 (rates down into the 40s can be normal, and asymptomatic rates into the low 30s are not a cause for concern, even though they are clearly outside of average. The "Early Repolarization" doesn't really mean anything (it's descriptive rather than a diagnosis), but it is much more common in people in their teens and early 20s.I agree with everything in the interpretation except for the "Borderline" (I would have said "Normal"), but it's important to know why the EKG was done, as various conditions can masquerade as normal. (If this was a "routine" study, then you are paying the penalty for someone ordering a test that wasn't needed (unless you're an airline pilot or astronaut), getting a result that causes unnecessary concern.
Let me know if you have any more questions.
Your EKG is not at all suggestive of ischemia; your doc may have been thinking of the EKG changes seen in early in the minutes of a heart attack (which bear a superficial resemblance to early repolarization). But that's not what your EKG showed. :)
I have no idea why you have your spells of reduced exercise tolerance, but I believe it's unlikely to be related to a heart problem (else your stress test would have shown clear abnormalities; and also because heart problems don't come and go like you described).
Could drinking too much water cause poorer heart performance by diluting electrolytes or anything like that? Or could some other blood/body chemical changes?
Or could flareups of colitis?