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  • (02) 8319 5555

Heartworm in Dogs

It’s easy to overlook heartworm prevention, but it can leave your dog at risk of a deadly disease.




What is a Heartworm?  

‘Dirofilaria immitis’ Heartworms are long, thin parasitic worms that look like strands of spaghetti. They live in a dog’s heart and lungs, where they grow up to 30cm in length. When these worms become big enough, they clog up the heart and major blood vessels, causing heartworm disease. It causes incredible suffering and sadly, can prove fatal.


How is heartworm transmitted to dogs?

Heartworm is not spread directly from dog to dog, but via mosquitoes.

When a mosquito bites a dog that’s infected with heartworm, it picks up tiny larvae, which it then spreads to other dogs when it bites them. Once in the bloodstream, these larvae mature into adult heartworms. They have the potential to wreak havoc on the heart, lungs and other organs. It may take a number of years for dogs to show signs of infestation.


How does heartworm affect my dog and what are the signs?

Adult worms cause disease by clogging the heart and major blood vessels. This can lead to a reduction in blood supply to vital organs and subsequent organ dysfunction. Young worms (microfilariae) tend to block the smaller blood vessels and may cause vascular disease.


Signs include:

  • a soft, dry, chronic cough
  • swelling of the abdomen
  • shortness of breath and reluctance to exercise
  • lethargy or listlessness
  • weight loss
  • just “not doing well”

Unfortunately some dogs do not show any signs. In these animals the only sign may be sudden death.


Diagnosis of heartworm in dogs

In the majority of cases, heartworm can be diagnosed by a simple blood test performed by your veterinarian. Depending on the severity of signs, other tests to determine the severity of heart worm disease may include:

  • a complete blood count and biochemistry to assess organ function
  • chest X-rays (radiographs) to assess the impact of heartworm on the heart and lungs
  • chest ultrasound


Sydney Animal Hospitals’ approach to prevention of dog heartworm

Because heartworm disease is a life-threatening condition and can be challenging to treat, prevention is vital for the wellbeing of your dog. As heartworm has a complex life cycle and is spread by mosquitoes that are ubiquitous in the environment, year-round prevention is essential.



At Sydney Animal Hospitals, we recommend an annual injection to ensure your dog is protected against heartworm. 

Use of an annual heartworm injection means that: 

  • You never have to worry about missing a monthly treatment and thus risk exposure to heartworm.
  • Your dog only requires a simple, easy treatment once a year.
  • You don’t have to worry about administering tablets or spot-on treatments.



Call your local Sydney Animal Hospital to discuss a tailored heartworm prevention program for your dog.  

Newtown (02)9519 4111
Inner West (02)9516 1466
Norwest (02)8883 0411
Kellyville (02)8883 0533
Newport (02)9997 4609
Avalon (02)9918 0833 




#HeartwormPrevention #AnnualInjection