Our lab ZsaZsa has always suffered from the heat, despite being born in Italy. Now she is ten, it is even worse and although there has hardly been any hot weather to speak of so far this year, she still has panting fits.
I have found the best solution for her is to drape her in a towel that has been soaked in cold water and wrung out. She looks rather Mata Hari-ish, but it does seem to cool her instantly and have a very soporific effect, like an instant tranquiliser!
At night I sleep with the windows open and drape her in her towel then turn on a floor standing fan. She is quite capable of shaking the towel off and moving away from the fan if she wants, but I have found she just likes the sensation and crashes out.
Read about the dangers of heatstroke here.