That is a huge problem out here in the arid desert. High temps combined with the natural dehydration that takes place will cause issues. I make sure I pace myself in that I limit excess movement. If I walk out to a ball, I carry all the clubs I think I will need so I don't have to make extra trips to the cart. Around the greens, I always carry a club and putter so I don't have to make an extra trip. I limit practice swings. I move more slowly. I drink lots of water or Gatorade. I make sure I keep my head covered and spend as much time in the shade as possible.