I always say summer is NOT our best season. I walk Makita after the sun has went down and usually in evening hours. But some nights, if it is too hot, we don't go. I've found that even now, for example yesterday was only mild 60's, if the humidity is up then she's panting after the walk.
Keep the walks shorter too and take a break if you have to. I will actually put Makita in a sit for a couple minutes (although she's 6, not a young thing anymore) just to get her breathing slowed back down. Its a good time to teach them sit, then I use the command "wait" (you can use whatever)...
If they are outside, always have fresh cool water (put ice cubes in the water, some dogs love them) available. My girl stays indoors though. Its just not worth taking the chance.
Just compare it to standing outside yourself, covered in a black shirt, and pants, with the sun beating down on you....
Also, I don't take her on car rides unless we are going somewhere and blasting the AC for a short trip through a drive through or something.
It takes a very short time for them to get overheated.
Best to play it safe.
