How to Tell if a Dog is in Heat Pictures (9 Photos)

If you’re keeping an unspayed female dog as a pet at home, then the time will come when she is in heat.

Knowing when to expect this and the signs to look out for will not only help you plan in advance but also prepare you to help your pet.

It’s worth noting that dogs, unlike cats in heat, experience more discharge when in heat and ready to mate.

So, how can you tell if your dog is in heat and what should you do to help? Below we share pictures to help you tell if a dog is in heat and what signs you need to look out for.

How to tell if a dog is in heat pictures

There are many behavioral and physical changes that will help you know when your dog is in heat. Below we share pictures to help you tell when a dog is in heat.

1. Swollen vulva

How to tell if a dog is in heat pictures

One of the first signs a dog is in heat is a swollen vulva. This happens when due to the increase in estrogen levels in preparation for ovulation. This happens during the first stage of a dog’s estrous cycle (heat cycle), referred to as the proestrus phase.

2. Blood-tinged discharge

How to tell if a dog is in heat pictures blood tinged discharge symptoms

This also happens during the proestrus phase. You will notice small amounts of blood-tinged  discharge. If your dog is in heat and you notice this then there’s no need to worry at all. Make sure the dog is not bleeding too much as this could indicate a serious health problem.

3. Excessive licking of the genital area

How to tell if a dog is in heat pictures

If you notice your female dog is constantly licking her genital area and showing other signs such as a swollen vulva and blood-tinged discharge, she’s in heat. This sign is among the common behaviors of a female dog in heat that becomes evident during the proestrus phase of the canine estrus cycle.

4. Receptive to male dogs sniffing and licking the vulva

How to Tell if a Dog is in Heat Pictures

Another way to tell your female dog is in heat is her receptiveness to male dogs sniffing and licking her vulva. This is probably the surest way to tell a dog is in heat and is seen during the first phase of the estrus cycle.

5. Frequent urination in the presence of male dogs

How to tell if a dog is in heat pictures

A female dog in heat will be more comfortable urinating in the presence of male dogs. Urination will be more frequent and very irregular. This is observed during both the proestrus and estrus phases of the heat cycle (1st and 2nd phases).

6. Postural changes and change in tail position

How to tell if a dog is in heat pictures
How to tell if a dog is in heat pictures

During the first phase of the heat cycle, the female dog will hold her tail close to her body. However, she will hold her tail slightly raised and to the side in the second stage of the heat cycle. She will also adopt new postural changes aimed at attracting male dogs for mating.

7. Excessive wagging of the tail

How to tell if a dog is in heat pictures

This is another flirting-like behavior towards male dogs that occurs during the second stage of the heat cycle. The dog will wag its tail excessively, especially in the presence of a male dog. Dogs typically wag their tails when being friendly or welcoming to humans or other dogs.

8. Agitated, aggressive, or nesting behavior

How to tell if a dog is in heat pictures
How to tell if a dog is in heat pictures

A dog in heat will also portray signs of agitation, aggression, and nervousness and happens during the second phase of the heat cycle. This is the stage when the dog is ready to mate.

9. Increased physical activity, e.g. mounting behavior

ways to tell if a dog is in heat
Female dog mounting a male dog’s head

This is another behavioral change dogs in heat portray. It happens during the estrus phase and will be hyperactive, including mounting other dogs, both male and female.

Below are the 4 stages/phases of a dog’s heat cycle.

What are the stages of a dog heat cycle?

The dog’s heat cycle also called the estrus cycle is comprised of four distinct phases, each bearing unique physical and behavioral changes that allow you to tell the stage your dog is at. The four stages of a dog’s heat cycle are:

1. Proestrus phase

This is the phase when estrogen levels rise in preparation for ovulation. Signs seen during this phase include a swollen vulva, blood-tinged discharge, excessive licking of the genital area, aggression towards male dogs, and a change in tail position with the dog holding it close to the body. This phase lasts anywhere from one to four weeks.

2. Estrus phase

This phase is also known as “heat” and it’s the stage your female dog is ready to mate and will be more receptive to male dogs. Progesterone levels rise and estrogen levels drop in preparation for pregnancy. Signs seen during this phase include frequent urination, drop in discharge, color change in discharge, flirting-like behavior towards male dogs, and holding the tail to the side. This phase lasts anywhere from a few days to 21 days, the average being 9 days.

3. Diestrus phase

This phase happens immediately after the “heat phase” is over. It allows the dog’s body to develop pregnancy or return to normal in case there is no successful mating. The vulva will return to normal size and discharge will disappear.

4. Anestrus phase

This is the cessation phase where estrogen falls back to usual levels and progesterone levels will drop to normal if successful mating was not achieved (i.e. the dog did not become pregnant). There are no behavioral changes associated with this phase.

When do dogs go into heat for the first time?

The age at which a dog goes into heat for the first time varies between breeds. Small breeds experience the first heat cycle at six months of age while large breeds experience the first heat cycle when they are fifteen to eighteen months old.

How long do dogs stay in heat?

Dogs stay in heat for an average of 9 days, with some being in the “heat phase” for two to three weeks. The “heat phase” is the phase when the dog is ready to mate and can get pregnant. The length of the “heat phase” or “estrus phase” varies between breeds.

How often will my dog go into heat?

Most dog breeds go into heat twice a year, roughly six months apart. Small breeds may go into heat three times a year while giant breeds may cycle only once a year. The heat cycles are likely to be irregular if the female dog is still very young or is very old.

Do female dogs smell when in heat?

Yes. Female dogs produce a unique smell when in heat that male dogs find alluring. The smell is a result of the release of pheromones by the female dog ready to mate and helps attract male dogs. Luckily, this smell is natural and harmless for a female dog in heat.

Is my dog in pain when in heat?

Dogs do not experience pain when in heat because they do not go through menstrual periods, as humans do. However, the first phase of the estrus cycle (heat cycle) is characterized by aggression towards male dogs because the female dog is not ready to mate.

What should I do if my dog is in heat?

What to do when your female dog is in heat largely depends on whether you want her to mate or not. In case you’re not ready for puppies yet and mating isn’t an option, you should do the following:

  • Do not let your female dog out alone in the yard. She releases pheromones that attract male dogs when she is ready to mate. That’s how easy it is for male dogs to know a female dog is looking for a mating partner.
  • Do not let your dog off the leash. If she breaks loose, the hormones and desire to mate will drive her into finding a male dog within minutes.
  • Consult your vet if you notice signs of illness, especially if your dog is old. Old dogs are more likely to experience health issues during and after heat, pyometra being one of them. It’s an infection of the uterus and the uterus is filled with pus.
  • Ensure your dog’s ID tags and microchip information are up-to-date. These details come in handy in the event your fluffy friend escapes and you can’t locate her.

How to take care of a dog in heat

Some actionable ideas to take care of a dog in heat include:

  • Investing in good disposable and/or reusable dog diapers
  • Designating a good blanket for use during this period
  • Do quick cleanup with disposable swipes to prevent carpets from getting soiled
  • Cuddle your fluffy friend once in a while (if she is okay with it)
  • Offer safe, chew-resistant toys to keep them engaged and prevent boredom
  • Make sure she’s eating well and drinking plenty of water
  • Ensure she gets the necessary potty breaks whenever in need


We have shared nine pictures on how to tell if a dog is in heat. If you have an unspayed female dog, then always be on the lookout for the signs to know when she’s in heat. You should also ensure she’s is eating well and drinking enough water to remain healthy and full of energy.

Video Credit – Love My Pups.

Video Credit – Millie a Cockapoo.


  1. Thanks for explaining that a little bloody discharge can also be a sign of a god being in heat. I’d like to take my dog to a pet clinic soon because she hasn’t been eating much ever since she starting being in heat. I’m a bit worried about that.

    1. Hi Alice, there are instances when a dog in heat experiences a decreased appetite. It is normal and quite common. You should, however, have her checked if she goes longer than 48 hrs without eating anything.

  2. My 10 month old puppy is in heat now for 2 weeks. When should I get her spayed (she went into heat the day before her spay was scheduled:(

    1. Hi Cathi, you need to wait until your puppy is out of heat and all four estrus phases are complete. This period differs by breed, often between 1 and 2 months. I would recommend seeking veterinary advice to know the ideal time to spay her once she’s out of the heat.

  3. My 13 lb dog is just finishing her first heat. Along with the enlarged vulva, her fur with in about 2″-3″ around her vulva has grown denser and about twice as long as her normal fur. I know her vulva will decrease in size, but will her now long fur be replaced by normal length fur? Is it OK to trim it back with the surrounding fir? — I find the extra length fur highlights her vulva area, and is personally unbecoming.

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