Heat Stroke in Dogs


The following are real life cases of Heat Stroke in Dogs that have been treated by Dr. Mike Richards, DVM.

Heat Stroke - Signs and Prevention
Heat Stroke Death or Addison's Disease

Heat Stroke - Signs and Prevention


I am a guide dog user who lives in Florida. As you know it gets extremely hot and humid here during the summer months. If I am working my dog outside during the day (which I do not really like doing but have to occasionally) what should I watch for in order to prevent heat stroke and are there any precautions, i.e. water that I can take?


I will try to research this topic in case there is additional information that might help. It is important to make sure that Mia stays hydrated, so bringing along water is a good idea. To allow access to cold water it can be helpful to freeze water in a bottle and to give it in small amounts as it melts. This works pretty well using the plastic bottles that water comes in except that it often deforms them enough that they won't stand up on their own, making it necessary to keep them in some kind of holder or to replace the top carefully with each use.

Signs of heat exhaustion include:

  • heavy panting
  • hyperventilation (deep breathing)
  • increased salivation early then dry gums as the heat prostration progresses
  • weakness
  • confusion or inattention
  • vomiting or diarrhea
  • sometimes bleeding

As the condition progresses towards heat prostration or heat stroke there may be:

  • obvious paleness or graying to the gums ( I realize this sign won't work for you but you might keep it in mind to ask someone about, just in case)
  • shallowing of the breathing efforts 
  • slowed or absent breathing efforts
  • vomiting and diarrhea that may be bloody 
  • seizures or coma

Temperatures above 105 degrees Fahrenheit are dangerous, so you can check if you have a way of taking her temperature (most people don't carry around thermometers with them and the physical signs are usually enough to go by). If you are familiar with how quickly and deeply Mia breathes when she is comfortable and after a walk on a cool day you can use that information to judge when she is breathing harder than normal on a hot day.

The best approach to heat exhaustion is to prevent it by allowing acclimation to exercise on hot days slowly, to make sure there is access to water and to retreat to air conditioned areas when signs of overheating first occur. In our practice we rarely see heat exhaustion on really hot days except for dogs who are trapped in cars, greenhouses or similar hot environments. Most dogs and people are smart enough not to overexert on those days.

We see problems the first moderately hot days of the summer in active dogs who just go on being really active on these days before they have a chance to get used to the heat. We also see problems here because people assume that if a dog is in the water, which they frequently are since we are near the Chesapeake Bay and numerous tributaries to it that the dog won't overheat. This just isn't true when the water temperature gets much above 75 degrees if the dog is working hard in the water.

If Mia should show signs of serious distress from the heat it is best to cool her immediately with cool or tepid water rather than really cold water. If ice packs are available they can be applied to areas where circulation is very good, such as the "armpits", inquinal region, or neck. Blowing air over her with a fan as you cool her off with water can be helpful. As soon as she seems to be gaining some comfort proceed to your vet's clinic. Dogs who suffer from heat stroke can develop delayed complications that are really serious, including death, if they are not properly monitored and cared for.

I hope that this helps some. If you have additional questions, please feel free to ask them.  

Check out an overview of Dog Heat Stroke Symptoms.

Heat Stroke Death or Addison's Disease


One of my questions relates to a 2 year old mastiff that I lost recently. He died within 24 hours of being at a kennel (1st time I had my dogs at a kennel). The autopsy said he died of heat stroke. His body temp, when the vet arrived at the kennel, was 109 degrees. The kennel employees were not there when the dog collapsed and suspect that he may have been down for about 5 m in. The kennel also admitted that they were dumb-founded when it occurred and hesitated to call the vet and instead called our housesitter and our manager at our business to see if he had a preexisting condition.

The reason I mention this is because they said it probably took about 25 min for them to administer 1st aid to my dog. They are claiming that although it was a very hot and humid day, they did not have my dog outside that long for him to have a heat stroke. The vet tech who arrived at the kennel stated that it was very warm inside the kennel also.

I guess I'm trying to learn more about heat stroke to make sense of this. I looked up on the Internet and it mostly talks about dogs being kept in cars. Could mastiff's be more susceptible to heat stroke? Also, our dogs are not kept outside and are exercised during cooler temp versus exposing them to extreme heat. Zeus was on Metronidazole, 500mg., for an upset stomach the week prior to his death. The autopsy showed that Zeus was in excellent health and his organs were normal. They did note that his adrenal glands were smaller than expected for his dog's size.

His behavior prior to his death on that date according to the kennel that he was playing happily with our 2 other dogs, had a good appetite, and seemed to be happy as indicated by his tail wagging and affection. My particular quesitons

  1. How long does it take for a dog's temp to reach 109 degrees (at the vet the week before his temp was normal)?
  2. How soon should a dog be cooled down when collapsing? Could cooling him down saved his life?
  3. Could the medication predispose him to a heat stroke (he took the doses recommended and was off it already for 2 days)?
  4. Did his smaller adrenal glands cause him to have a heat stroke?

I apologize for asking questions that may not have exact answers. I'm trying to learn as much as I can so to further prevent another death and to educate myself about dog safety. I also need closure to my buddies death and hope time and more information may help. Thank your for your time and invaluable service. 


There are two strong possibilities with the situation you describe. The first one is that your dog simply had heat stroke and that all symptoms and his death were related to that. The second is that he had hypoadrenocorticism, or Addison's disease, which can lead to sudden death without any other predisposing cause and also makes almost any other stressful condition much worse. So I'm going to divide this answer into two parts, one to cover the heat stroke and one to cover the Addison's disease to some extent.

Heat stroke in dogs is not all that uncommon. Dogs do not have an efficient method of handling heat stress because they don't sweat and they don't seem to figure out that they shouldn't get excited or work hard in the heat, either. Heat stroke is most common in the large breeds and in dogs with short noses, so mastiffs are in the group of dogs that are most susceptible to this problem.

Death from heat stroke can occur pretty quickly. The shortest interval between exposure to high heat extremes and death is about 20 minutes, based on our practice experience, but these have been "closed car" cases. It is probably more common for dogs to experience heat stroke in the first few days they are acclimating to heat and for it to occur in conjunction with excitement or exercise. Most dogs probably take an hour or more to develop heat stroke in these circumstances but if they were struggling with the heat prior to exercising it is possible that the problem could develop more quickly. Any illness that is contributing to an increase in body temperature can also shorten the time period for signs to become severe.

The most common clinical signs of heat stroke are:

  • weakness
  • loss of balance
  • excessive panting
  • roaring breathing sounds
  • excessive salivation
  • decrease in mental awareness
  • collapse and death

Any time that heat stroke is suspected it is best to get an immediate rectal temperature reading and to begin treatment immediately if the body temperature is over 106 degrees Fahrenheit or to stop all activity and move indoors if the temperature is less than this but elevated above 103.0 degrees Fahrenheit. Body temperatures over 107 degrees Fahrenheit are a critical emergency, because organ damage can occur at this temperature and at higher temperatures.

Treatment consists of cool water (not cold water) bathes or rinses. If the water is too cold, or if ice is used to cool a heat stroke victim it can cause a decrease or loss of skin circulation, which can delay cooling. This should be done immediately for a few minutes and then the dog should be taken to the veterinarian's office or to an emergency veterinary clinic immediately. Most dogs will not drink water at this stage of heat stroke and it is not a good idea to spend time trying to get them to. Just go to the vet's as quickly as possible. The veterinarian may want to use cool water enemas, cool water gastric lavage (rinsing of the stomach), corticosteroids and specialized intravenous fluid therapy using colloids to maintain blood pressure. If there is any evidence of disseminated intravascular coagulation (DIC), intensive therapy for several days may be necessary if a successful outcome is possible.

Immediate treatment is critical to success when dealing with heat stroke, so delays are potentially harmful, or fatal. Many people do not associate the clinical signs they are seeing with heat stroke, though. Especially when their level of suspicion is not high. We have seen heat stroke in dogs who were swimming or who were merely excited but not obviously exercising hard, situations in which people often do not make an association with heat stroke. We have even had one bulldog patient who developed heat stroke in the house, with the air conditioning on, apparently because he became very excited about guests at the house for a party.

So heat stroke could easily be the whole problem.

On the other hand, small adrenal glands can be a sign of hypoadrenocorticism, or Addison's disease. In this disease there is a deficiency in the production of corticosteroids and mineralocorticoids (regulate electrolytes in the body). Patients with Addison's disease often have very vague signs of illness that is often chronic. Often these signs are vague enough that owners don't recognize them or don't seek treatment for them.

The range of signs is large, but includes:

  • intermittent decreases in appetite, or dogs with a generally poor appetite
  • vomiting
  • diarrhea
  • muscular weakness
  • depression or lethargy
  • slow heart rates
  • increased drinking and urinating
  • cardiac arrhythmias
  • unexplained shock and sudden death

Most patients probably only have one or two of these signs at any given time and will never develop all of them.

Patients who respond poorly to stressful situations and especially patients who die from stress that most patients have no trouble handling are likely candidates for Addison's disease. It is likely that most veterinary patients with Addison's disease are diagnosed by accident when blood is drawn for other reasons or have their Addison's disease diagnosed only after a poor response to a stressful situation, such as their first surgery or a traumatic incident. Unfortunately, if they do progress to severe shock or death quickly, the diagnosis may not come in time.

I know of no link between the use of metronidazole and heat stroke, except that metronidazole can cause vomiting or diarrhea and any amount of dehydration induced by these conditions would lead to an increased possibility of heat stroke. I have not heard of any problems with the use of metronidazole in patients with Addison's disease. Overdosages of metronidazole (not likely at the dosage of 500mg once or twice a day in a mastiff) can cause slowing of the heart rate and that might make the slow heart rate associated with Addison's disease worse.

It is not possible at this point to really tell you if Addison's disease contributed to your mastiff's death but it does seem like it could have. On the other hand, prompt treatment for the high body temperature, along with intravenous fluid therapy, might have corrected both problems sufficiently enough to allow your dog to live through the crisis. Whether that would have actually helped enough is not certain, but it is definitely possible.

It is really hard to find yourself dealing with the loss of a pet when the loss seems unnecessary or partially due to human error, but we really are all susceptible to making bad judgments and once that process starts it seems to just induce further bad judgments in a vicious cycle, in some cases. Hopefully, the folks at the kennel will learn from this experience and use the information to prevent a future occurrence, someday—or at least to get treatment promptly if they see these signs again.

It is very helpful if you spell out what you want done in an emergency with any kennel you may deal with in the future. It also helps to figure out transportation plans for a pet to get from the kennel to the veterinary hospital, when necessary. Having a friend who is willing to be "on call" can really help. Getting directions from your vet for what to do after hours and on weekends or holidays is important, too. If the kennel ever needs to take a pet to the emergency clinic, or make arrangements for the pet to get there, it can help a lot if it is clear that you want them to do that and if you have left a deposit to go towards emergency veterinary care, if you have reason to suspect it might be necessary. I hope that this information is helpful to you. It is so hard when a young pet dies unexpectedly, especially when it wasn't possible to be with them to make all the decisions that had to be made.

Check out an overview on Addison's Disease.


Michael Richards, D.V.M. co-owns a small animal general veterinary practice in rural tidewater Virginia. Dr. Richards graduated from Iowa State University's College of Veterinary Medicine in 1979, and has been in private practice ever since. Dr. Richards has been the director of the PetCare Forum...