What do you call a dog that's hot?

A dog that's hot is often referred to as being "in heat" or "in season," indicating that it is in the reproductive phase of its cycle. This term is typically used for female dogs, which experience estrus, during which they can attract males and may exhibit certain behaviors related to mating. If you're referring to a dog feeling hot due to temperature, you might simply say the dog is "overheated" or "too warm."