Heat stroke in dogs typically starts with heavy, frantic panting and excessive drooling, then quickly progresses to weakness, confusion, vomiting, and collapse. A dog’s normal body temperature sits between 101°F and 102.5°F. At 104°F, a dog is in moderate heat stroke and needs immediate help. At 106°F, the situation is a dire emergency with organ damage already underway.
Recognizing the signs early is the difference between a scary afternoon and a fatal one. Here’s what to watch for at each stage and what to do about it.
Early Warning Signs
The first thing you’ll notice is panting that looks different from normal post-exercise breathing. It’s louder, faster, and the dog can’t seem to settle. The tongue may hang far out of the mouth, and you’ll see thick, ropy drool. Your dog may start seeking shade obsessively, lying flat on cool surfaces, or refusing to walk further. These are signs of heat exhaustion, the stage right before heat stroke, and your window to intervene before things get dangerous.
At this point, the dog’s body is still trying to cool itself. Dogs can’t sweat through most of their skin the way humans do. They rely almost entirely on panting, which pushes air across the moist surfaces inside the nose and mouth to evaporate heat away. When the air is too hot or too humid for that system to work, body temperature starts climbing fast.
What Full Heat Stroke Looks Like
Once a dog crosses into actual heat stroke, the signs become more alarming and harder to miss. You may see:
- Bright red or muddy gums. The gums and tongue may look deep red at first as blood vessels dilate, then shift to pale, gray, or bluish as the body goes into shock.
- Stumbling or wobbly movement. The dog may walk like it’s drunk, bump into things, or seem unable to stand.
- Confusion or “glassy” eyes. The dog may not respond to its name, stare blankly, or seem disoriented, almost delirious.
- Vomiting or diarrhea. This can come on suddenly and may contain blood, which signals the gut lining is being damaged.
- Collapse. The dog goes down and can’t or won’t get up.
Neurological problems are present in nearly every confirmed case of heat stroke. In a study of dogs with clinical heat stroke, 40% were comatose, 35% had seizures, and 33% were in a stupor. Milder cases still showed disorientation or delirium-like behavior. If your dog is having a seizure, losing consciousness, or can’t stand, the situation is critical.
What’s Happening Inside the Body
The visible signs are only part of the picture. Heat stroke is a multi-organ crisis, and some of the most dangerous damage isn’t obvious from the outside.
When body temperature spikes, blood flow redirects toward the skin to try to release heat. That means less blood reaches the gut, kidneys, and brain. The intestinal lining, starved of oxygen, starts breaking down. Bacteria from the gut can leak into the bloodstream, triggering a system-wide inflammatory response. This is why bloody diarrhea is such a red flag: it means the intestinal barrier is already failing.
The kidneys take a direct hit from the heat itself, from dehydration, and from the toxic byproducts of muscle breakdown. Kidney injury can be subtle at first and may not show up until hours after the initial episode, which is why dogs that seem to recover still need veterinary monitoring. Kidney damage within the first 24 hours is an independent risk factor for death.
The brain is equally vulnerable. Extreme heat causes swelling, reduced blood flow, and in fatal cases, bleeding and tissue death. This is what drives the seizures, coma, and behavioral changes you see from the outside.
Breeds at Higher Risk
Flat-faced (brachycephalic) breeds are significantly more vulnerable to heat stroke because their shortened airways make panting less efficient. The cooling system in a dog’s nose depends on surface area inside the nasal passages. Breeds with compressed skulls simply have less of it. A large UK study found that brachycephalic dogs had roughly twice the odds of heat-related illness compared to dogs with medium-length skulls.
Five breeds stood out with significantly increased risk: Bulldogs, French Bulldogs, Dogues de Bordeaux, Cavalier King Charles Spaniels, and Pugs. Boxers trended toward higher risk as well. If you have one of these breeds, heat stroke can develop faster and at lower temperatures than you might expect. Overweight dogs and older dogs with heart or respiratory conditions also face elevated risk regardless of breed.
What to Do While Cooling Your Dog
The current guideline is “cool first, transport second.” Starting to lower your dog’s temperature before you drive to the vet can save its life. Here’s how to do it safely.
Move the dog to shade or air conditioning immediately. If you can, submerge the dog’s body (not the head) in cool water. Cold-water immersion is the fastest cooling method for young, otherwise healthy dogs. For older dogs or those with other health problems, spraying the coat with water and pointing a fan at the dog (evaporative cooling) is a safer approach. You can also place wet towels on the dog or offer cool water to drink if the dog is conscious enough to swallow.
There are two important things to avoid. First, don’t use ice-cold water or ice baths. Experimental studies found that some dogs died from cardiovascular collapse when immersed in ice water, likely because the extreme cold caused blood vessels near the skin to constrict, trapping heat in the core. Use cold tap water or cool water instead. Second, don’t apply rubbing alcohol to the paw pads, an old trick that’s fallen out of favor. It can actually constrict surface blood vessels and trap heat, doing the opposite of what you need. It also poses a toxicity risk.
Stop active cooling once the dog’s temperature drops to about 103°F. Overcooling is a real danger because the body’s temperature will continue to fall even after you stop, and hypothermia brings its own set of problems.
Why Veterinary Care Still Matters After Cooling
Even if your dog perks up and seems fine after cooling, organ damage may already be underway. Kidney injury from heat stroke is often mild enough to go unnoticed at first, but it can progress to full kidney failure over the following hours or days. The gut damage that allows bacteria into the bloodstream can trigger a delayed inflammatory cascade. Brain swelling may worsen before it improves.
At the vet, your dog will likely receive fluids and be monitored for signs of clotting problems, kidney function changes, and ongoing neurological issues. The first 24 to 48 hours after a heat stroke episode are the most critical for catching complications early. Dogs that receive prompt cooling and veterinary support have a much better chance of full recovery than those where treatment is delayed, but heat stroke remains a life-threatening emergency with a meaningful fatality rate even with treatment.