Signs of Heartworm in Dogs

As a dog owner, you’ve probably heard about heartworm and all the ways you can prevent it from happening in your dog. But do you know what heartworms actually are or why you should be preventing them?

How do they even get to your dog? Heartworms are dangerous and sometimes even fatal for your dog, but how do you know if your dog has them? Here’s what you need to know about heartworms for your dog, and how to prevent them.

What are heartworms?

Heartworm disease is a very serious and sometimes fatal disease for your beloved four legged family members. The worm part of this comes from foot long worms that inhabit your dog’s heart, lungs and blood vessels and can lead to severe long-term consequences for your dog.

While we primarily associate heartworm disease with dogs and cats, they have been known to live in wolves, coyotes and foxes. Since these animals often live in close proximity to the urban areas most dogs live in, they have been identified as predominant carriers of this disease.

How does my dog get heartworms?

Thankfully, this is a completely preventable illness but that doesn’t mean your dog won’t contract it without proper prevention.

Dog Heartworm


Heartworms are transmitted through mosquito bites, but only when a mosquito bites and draws blood from an already infected animal. The mosquito will take in heartworm babies – microfilariae – with the blood it takes from an animal, and those babies will develop while inside the mosquito and then be transmitted to the next animal the mosquito bites.

Temperature also plays a large role in the transmission of this disease. Typically, the biggest risk in Canada is when the summer months come and the higher risk areas include those that experience humid summer months.

How long until my dog shows symptoms if they have heartworms?

One of the worst things about this condition for dogs is that this illness doesn’t show up and symptoms aren’t present until about 6 months after the dog has been infected.

Unfortunately, when the symptoms finally show it means the disease has spread and the worms have reached maturity. This also means it can be very dangerous for your dog.

You might also like to read about: Symptoms of Diabetes in Dogs

What are the symptoms of heartworms?

The symptoms of heartworms can, unfortunately, also be signs of other disease in dogs but early detection and close watching of your dog can help a lot in treating this condition.

Once the worms have developed fully and have invaded your dog’s heart and lungs, your dog will have very visible and obvious symptoms.

Here’s what you need to watch for early on in the progression of heartworms

Regular and persistent cough

Many dogs will experience kennel cough, at some point, and the cough associated with that is strong and sporadic. With heartworms, the cough will be much more dry.

Early on, with heartworms, the cough will be present with even small amounts of exercise as this is when the worms make their way into the lungs of your dog and cause a blockage.


Does your dog love to go for a good run or play in the backyard, but suddenly they don’t have any interest in doing those? This can be a sign of having heartworms as this conditions means any kind of physical activity will be very strenuous and difficult for your dog.

Weight Loss

With heartworms, doing any kind of activity will become increasingly difficult for your dog as the condition worsens. This can include getting enough energy to even just get up and eat, which means your dog will have unexplained weight loss.

Laboured Breathing

Along with persistent coughing, issues with breathing can become evident as the condition progresses in your dog. This condition can cause fluid to build up around blood vessels in the lungs, which makes it hard for the lungs to oxygenate blood.

Protruding Ribs

This condition causes fluid to build up around the lungs of your dog, and this can cause your dog’s chest to look like it’s protruding. In addition to this, your dog’s ribs might look like their bulging due to the weight loss associated with this condition.

Late Stage Symptoms

The symptoms listed previously are usually associated with early and mid-stage development of heartworm, and there are additional symptoms you may notice that mean the condition has developed into a late stage situation.

In the later stages, the symptoms mentioned will become much more obvious and severe. Additionally, your dog could experience

    • Abnormal breathing sounds
    • Enlarged liver
    • Heart murmur

Dog Heartworm


What is the treatment for heartworm?

If your dog has been diagnosed with heartworms, the treatment isn’t as easy as it can be for other conditions. The goal is to kill all the adult and immature worms before they continue to spread and to keep the symptoms and long-term problems to a minimum.

The treatment can be incredibly expensive, compared to other conditions. The recovery process is long, difficult and can be very painful for your dog. There is no promise or guarantee that your dog will be completely cured of this disease, even with treatment and when it’s caught early.

While you’re doing is going through treatment for heartworm, here’s what you need to know

Confirm the diagnosis

Your vet will do an antigen test, but the diagnosis should be confirmed with an additional, different test. The treatment for heartworm is complex and very expensive, so you and your vet will want to be absolutely sure of the diagnosis.

Limit Activity

For some dogs, this is going to be very difficult. You’ll need to restrict exercise as soon as the diagnosis is confirmed for your dog.

This is because physical activity increases the rate at which the heartworms spread and cause damage to the heart and lungs. The more severe or progressed the symptoms are, the more you need to restrict activity.

Stabilize the Disease

Depending on your dog’s symptoms and progression, your vet might need to stabilize your dog’s condition with additional treatments. When the disease is serious, it can take a couple months.

Start Treatment

Your vet will determine the right kind of treatment for your dog, depending on the development of the condition and your dog’s symptoms. Dogs with mild symptoms have incredibly high rates of successful treatment, but the severity of symptoms may not equate with how much the disease has progressed. Severe cases can also be treated successfully, but sometimes have long-term complications.

Start Prevention

About 6 months after treatment has been deemed successful and stopped, you can start administering prevention for your dog again. Your vet will do another test to make sure your dog is completely free of heartworms before starting the prevention. Make sure your vet also does a test annually so your dog doesn’t contract it again.

With this in mind, the best option for all dog owners is to make sure you have adequate prevention in place against heartworms.

You might also like to read about: What can I Give my Dog for Pain Relief? My Pet Is Not Well

How do I prevent my dog from getting heartworm?

During your dog’s yearly check up, your vet will likely recommend they do a heartworm test on your dog. This test involves drawing some blood from your dog and either sending it off or testing it in the office (if your vet’s office has the technology to do so). Your vet will call you with the results.

Based on your dog’s age, health and risk of exposure your vet will recommend how often to test your dog and what kind of prevention is best.

Even when your dog is on regular prevention, yearly testing is necessary and should not be neglected. The symptoms of heartworm disease don’t show up until about 6 months after infection, and by then the worms have matured and spread. Regular testing can catch the infection early – before symptoms – and that means the treatment can start even earlier.


What if I live where it’s colder?

While regions that experience more moderate or warmer climates seem to have more cases of heartworms that doesn’t mean it doesn’t happen everywhere.

The best option for your dog is always going to be prevention, but the plan for your dog should be discussed with your vet. Your vet will know the best course of action for your dog, and you should always consult with your vet if you have additional questions.

We want the very best for our dogs, and we want to make sure they live their very best life with us possible. With regular checkups and ensuring you use the prevention regimen prescribed by your vet, your dog has a great chance of living a long, healthy life without heartworms.

On the other hand, if your dog does contract heartworms, there are medical treatments with incredibly high success rates for your dog and they can completely recover to live a healthy and active life.

If you have any questions or are concerned that your dog might be heartworm positive you should contact your vet, and make an appointment for your dog to be checked as soon as possible!

You might also like to read about: Symptoms of Intestinal Blockage in Dogs