Not only the heat, but like down here in the South, humidity can affect any dog quickly. Tragically, several K9s in Indiana didn’t make it when the AC broke on the cargo truck they were being transported in. See the story here Dogs die from heat distress: Multiple K-9 officers killed in Northwest Indiana (wgntv.com)
Dogs overheat quickly because they do not sweat like humans do, so they pant.
According to a post from the AKC, here are some symptoms of overheating.
“As a dog’s temperature rises, blood rushes to the surfaces of the tongue, gums, and membranes to help transfer excess heat. Frantic panting, extreme salivation, bright-red membranes, and labored breathing are clear warning signs that your dog is overheated and may quickly progress to a metabolic meltdown as his temperature rises to over 106 degrees Fahrenheit and he can no longer cool themself.
He may gasp for air, and the entire mouth will become grayish to purple because of the unmet oxygen demand. As he dehydrates, the saliva thickens, and he may vomit and have diarrhea. Unable to stand, he may have a seizure, become comatose, and die. Even if you can cool him and he acts normal, rush him to an emergency clinic because his organs may have already been damaged and death could follow.”
– Dogs Overheating: Signs, Symptoms, & Prevention (akc.org)
Remember, if you are sweating, your dog is already uncomfortable and must work much harder to cool down by panting.