I was in LV for my birthday (July 30) last year. The heat isn't that bad -- I'm okay until 112 or above. But drink water. Lots of water.
Two stories: One of the first times I was in LV, I walked about nine miles to familiarize myself with the place. It was summer, I felt fine, then got all wobbly at the end. No wonder -- I had dropped about eight pounds! And because I wasn't sweating, I wasn't aware.
I went jogging two years ago -- summer about eight in the morning. It was amazing -- I could feel rivulets of sweat trickling down my face, but they almost instantly dried and I could feel the coolness where they evaporated. Like little icy streams down my face!! Then instantly gone. That tells you how fast you dehydrate if you exert in the heat.