One on my miniature hampsers is squeaking and panting?

i have two 11 month old miniature hamsters (not sure what breed but there both white underneath with grey/creme/brown bits on top, and there quite short and fat) and one's fur looks kind of sweaty and its squeaking constantly now (which started a week ago, when it squeaked constantly for 10 minutes on and off) and looks like its panting or heart beating very obviously and fast. the other hampsters fur looks abit sweaty but isnt squeaking or panting atall. weve just had a heatwave and i tried to keep their cage as cool as possible but it must have been quite hot in there still as i was attending to my other animals and couldnt sit with hampsters all day! what could be worng with him, is he dying?