No issues with heat in my national...Of course, San Diego never gets much over 80 degrees anyway!
Seriously....as Mike noted....water, water, water....I like to mix in a sports drink once in a while for some flavor, but water is the best.
I also find that keeping a towel in a cooler with ice is a refreshing wipe down between innings.
There are a couple of other things I have heard, but do not have personal experience with....one buddy of mine buys the individual powder packets of Pedialyte and mixes those in a water bottle...he says it's better than the sports drinks for electrolytes without as much sugar. I've also heard good things about the spirits of ammonia towels. I'm pretty sure we have discussed those here before.
Just remember that no matter where you live and work and how used to the heat you are, it can still affect anybody. The players and coaches get to sit in the shaded dugout for half the game, the blues don't have that option. Be careful out there and take care of yourself and your crews.