Heartworms in dogs: all the facts for pet owners

Heartworm in dogs is a serious health issue that can be fatal.  Learn how you can keep your dog safe.


Why you should take heartworm in dogs seriously

Heartworm in dogs is prevalent across Australia and can be a serious and potentially fatal condition. 
Knowing how to prevent heartworm is essential for all dog owners. Luckily, there is plenty you can do to keep your pooch safe and healthy.

Read on to learn what you need to know about heartworm in dogs. 

What are Heartworms?

Dog heartworms are a parasite spread by mosquitoes. The worms, which can grow to 30 cm in length, infest the heart, lungs, and associated blood vessels. 


The presence of heartworm in blood vessels causes inflammation and scarring, and may eventually lead to heart failure

heartworms in dogs
heartworms in dogs

Heartworm Symptoms in Dogs

As heartworm can be deadly, it is important to know if your dog is playing host to these parasites. 

There are often no signs of heartworm disease early on, however as the disease progresses increasingly severe signs may be seen. Here is a quick run down of heartworm symptoms in dogs:


  • Cough: Often one of the first signs of heartworm disease, coughing tends to be persistent and worsens with exercise. 


  • Lethargy and exercise intolerance: Dogs with heartworm disease tend to be less active than normal due to the compromising effect the worms have on the heart and lungs.


  • Weight loss: Weight loss can occur in dogs with heartworm disease.


  • Trouble breathing: If heartworm disease leads to heart failure, it can lead to a build-up of fluid in the lungs which makes breathing difficult.


  • Enlarged abdomen:  Heart failure can also cause a build-up of fluid in the abdomen (called ascites), giving affected dogs a pot-bellied appearance. 

It is important to note, that whilst the symptoms above can all be seen with heartworm disease, they are also seen in other conditions.  As always, please speak with your veterinarian for advice.

While puppies can be infested by heartworm from the bite of a mosquito, disease does not occur until the worms mature, which can take 6-7 months.  For this reason, heartworm disease is not seen in puppies less than 6 months of age.  

heartworm prevention
heartworm prevention

How do Dogs Get Heartworm?

Now that we know a little about heartworm, how do dogs get it? 

Heartworm are transmitted between dogs by mosquitoes. Adult female heartworm living in an infested dog produce tiny juvenile worms called microfilariae. When a mosquito takes a blood meal from a dog with circulating microfilariae, some of these are taken up. After a short period of development in the mosquito, these juvenile worms can be passed to a new dog when the mosquito takes another blood meal.  

Heartworm Treatment for Dogs

If you are worried that your dog might have heartworm, it is best to take them to the vet for testing, and if required, treatment. Remember, as noticeable symptoms of heartworm disease tend to arise quite late in the infestation, it is best to get your dog checked by your veterinarian at the first sign of illness.
Heartworm treatment for dogs diagnosed with adult heartworm infection involves the use of medications prescribed by your veterinarian. Treatment is not without risk, so it’s important to commence prevention treatments straight away to ensure they do not become re-infected.

Heartworm Prevention for Dogs

Luckily, over the counter heartworm prevention for dogs is readily available. For the best heartworm and flea prevention combined with additional protection from mites, ticks and intestinal worms, we recommend NexGard SPECTRA® for Dogs. For the best chewable heartworm tablets for dogs, try HEARTGARD30® PLUS, a combination wormer that not only protects against heartworm, but also hookworms and roundworms. It is important to commence heartworm prevention for puppies early in their life.  With NexGard SPECTRA for Dogs, heartworm prevention can begin from 8 weeks of age, ensuring your puppy is protected against heartworm from the get-go. 

Heartworm in Dogs FAQ

  • What are the side effects of heartworms? 

    Heartworms cause severe damage to a dog’s heart, lungs, and associated blood vessels. Signs associated with heartworm disease include:

    • Coughing 
    • Lethargy
    • Trouble breathing
    • Weight loss
  • How long can a dog live with heartworms? 

    How long a dog can live with heartworms varies greatly, depending on factors such as the number of worms present and the dog’s general health. Left untreated though, an infestation with these parasites can be fatal.

  • What are the first signs of heartworms in dogs? 

    Look out for coughing and lethargy, as these are two of the first signs that your dog has heartworms.

  • Can heartworms be passed from dog to dog? 

    Heartworms can’t be passed on by contact with other dogs. They can only be spread through the bite of a mosquito.

  • How do puppies get heartworms?

    A puppy will get heartworm by being bitten by a mosquito carrying microfilariae.

  • Do dogs poop out heartworms? 

    No, heartworms are not passed in faeces like some other worms.

  • How do humans get heartworms from dogs? 

    The same as with dog to dog transmission, humans can only get heartworms through mosquito bites. Heartworms don’t like to live in humans so cases are very rare.

  • Why is my dog coughing after heartworm treatment?

    If your dog is diagnosed with heartworm, the treatment administered by your vet kills worms present in the blood vessels of the lungs and can result in significant inflammation, leading to coughing.  If your dog has been treated for heartworm, strictly follow the advice of your vet.

  • Why is my dog vomiting after heartworm treatment?

    If you dog is diagnosed with heartworm, the treatment administered by your vet to kill the worms may be associated with side effects, including vomiting. There are many causes of vomiting in dogs. If your dog is vomiting after receiving vet-administered treatment for heartworm, it is best to contact them for advice.  

  • What is the cost of dog heartworm treatment?

    When a dog becomes infested with heartworm, treatment can be costly and not without risk, so prevention is a far wiser approach. Simple monthly dosing with NexGard SPECTRA for Dogs or HEARTGARD30  PLUS will prevent heartworm in dogs. 

Want more information on the treatments available for your dog or puppy?

Learn more about HEARTGARD30 PLUS and NexGard SPECTRA for Dogs for protection against heartworm and other parasites. 


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