Roblin Animal Hospital
Unit 104-4910 Roblin (corner of Roblin and Dieppe)

Monday - Friday 8am - 6pm
Saturday - 8:30am - 12:30pm

Roblin Animal Hospital/ Red River Spay and Neuter Clinic:

What are Heartworms?



Heartworms are large worms that are carried in the blood stram and live in the hearts of dogs and cats. It is a long, spaghetti-like worm that can be anywhere from 6 to 10 inches in length (~17 - 27 cm). This parasites name is Dirofilaria immitis. Dogs are the common host for this parasite.     

In Canada Heartworm infections are concentrated in southern Ontario, southern Manitoba and southern Quebec. In a 2010 Canada-wide study, 367,385 dogs were tested. From this number, 23,192 dogs were from Manitoba, of which 77 tested positive for this potential deadly parasite. These results show an increase of nearly 46% in the number dogs from Manitoba that tested positive for heartworm, based on the last study conducted in 2002.                                       

How are heartworms transmitted?

• Mosquito Bites
• Mother > Young

If transmitted from mother to it young the larvae live in the young’s blood but never mature to adult worms. Therefore they don’t harm the animal. However a mosquito can still pick up these larvae and transmit it to other animals. *The larvae must go through a mosquito host to become infective*. This means if that mosquito bites another dog and transmits the larvae, this new dog can now become infected with larvae that can mature into adult worms.

If transmitted to the animal by a mosquito it can infect the new host. These larvae can grow into adult worms in the blood stream. Generally these worms reside in the right side of the heart and can cause severe, sometimes irreversible, heart damage.

Heartworm can form in both dogs and cats. It tends to be seen less often in cats as the majority of cats spend less time outside and are therefore not exposed to mosquitoes as much.Heartworms need a mosquito to complete their life cycle.

What are the signs of heartworm disease?

The signs vary according to:

  • number of worms present
  • stage of life cycle
  • age
  • species of host.

The heartworms live primarily in the right side of the heart and lung.

Clinical Signs

  • Dog does not appear to be sick (the dog just acquired the disease)
  • cough, reluctance/inability to exercise
  • Severe shortness of breath, coughing, fainting episodes, weight loss, fever, abdominal swelling etc.


• Immiticides
Treatment of adult worms can be dangerous. Long term use of ivermectin can sometimes kill adult worms. However, these dead worms can start traveling through the blood stream and cause respiratory failure and death. Occasionally surgical removal of the worms is necessary. Adult worms and larvae must be treated separately.


  • We should first test your pet and find the heartworm status to be negative.
  • You can then begin heartworm prevention.
  • Prevention is in the form of a chewable monthly tablet, given in the summer months.
  • There are also topical monthly heartworm preventatives.
  • The most commonly prescribed oral heartworm preventatives are: Heartgard, Interceptor, Sentinel, and Revolution
  • Most of these preventatives also take care of other internal parasites.