Lauree Simmons, the founder and president of Big Dog Ranch, a no-kill rescue shelter with locations in Florida and Alabama, agrees. “Dogs can easily become overheated within 10 minutes,” she says, “especially the short-nosed dogs, like boxers, bulldogs, and French bulldogs.” Early signs of heat exhaustion in dogs include redness around the eyes and darkening of the gums and tongue, often to a deep dark red or purple (gums that are too pale, however, can also be a sign of heat exhaustion). Excessive salivating or panting is another key sign.