That's kind of scary - was it only your left hand? (side of your heart...)
I don't know, though. When I run (or used to, now that I can't) outside, I have to wear gloves because my hands always lose circulation. Maybe because the blood is pumping to your heart so much (and leg muscles, because those are being worked)? Sorry, I don't have a good answer, but I don't think it's that odd.
If you have heart concerns, I'd be worried. If not, then maybe not work so hard next time.