Heat is the worst thing for your guitar as far as actually killing it. Where hide glues might have been used, at about 120ish degrees (I forget exactly off the top of my head, but you can Google it) the glue will soften and pieces may come apart.

Other than that, you might need to tune more frequently just because the wood & metals & plastics will react to environmental changes at different rates. Temps in my area regularly swing 10 degrees Celsius from a.m. to p.m. and it`s not uncommon at all to go from 9 degrees overnight to 33 in the day. (That would be a 50 - 90 degree swing for you Fahrenheit folks.)

I have a variety of acoustics & electrics, and all of them survive fine. They need to. If they can`t live where I live, then they are not much good to me! :)