It's not just flat-faced dogs that are susceptible to the heat. ANY pet can overheat and end up suffering from heatstroke. Heatstroke (also known as heat exhaustion or heat stress), can occur very rapidly and can even be fatal.
It's crucial to remember that our pets can't perspire all over as humans do and they produce only a tiny amount of sweat through their footpads. They cool themselves down via panting but sometimes this isn't enough and they start to overheat.
The important point is that it doesn't necessarily need to be really hot or humid for heat exhaustion to occur and you need to be able to recognise the signs early and know what to do.