Phone: (02) 4832 1977 

Heartworm in Dogs

Heartworm is a particularly nasty parasite that’s spread by mosquitoes. When a mozzie bites a dog, it deposits larvae into the dog’s skin or bloodstream. These find their way to the dog’s heart, insidiously growing into long white worms up to 30cm in length and clogging the heart and vessels nearby, causing symptoms of heart failure. Treatment is difficult and expensive.

While heartworm distribution has spread significantly within Australia, Crookwell’s cold climate means our resident pets do not need regular heartworm medication. Originally detected only in the tropics and sub-tropics (Darwin and Brisbane, for example), the parasite is now routinely diagnosed in southern temperate areas.


If you plan to travel with your dog to heartworm areas outside Crookwell (this includes Sydney, the South and Central Coasts), either for a short holiday or on a regular basis, talk to our staff about heartworm preventative medication for your pet’s situation.

If you and your pet are travelling to known heartworm areas for periods up to 1 month, the current medication recommended is Guardian – this must be given immediately AFTER the pet returns home to Crookwell.

For pets staying in heartworm areas longer than 1 month, regular monthly treatments or a yearly injection are required.

Routine prevention

Dogs older than 6 months starting on heartworm prevention must be blood tested before heartworm preventative treatment can be started.

In puppies:

  • Start heartworm prevention at 12 weeks of age. Use either monthly tablets or start on a schedule of annual injections.
  • For injections, the first injection is given at 3 months of age, followed by a second injection at 6 months, then annual injections will provide ongoing protection.

We stock a range of heartworm products at CVH. Please talk to our staff about the best preventative schedule for your pet’s situation - new and more effective products are coming online regularly and it's important to ensure you are using the best possible preventative products to keep your pet safe. Note that many of these products also protect against other parasites such as intestinal worms (including whipworm and tapeworm), fleas, ear mites, sarcoptic mange and lice.