Pet Education

Browse our veterinary-reviewed Dog and Cat Illness Guide to learn more about pet health. Always talk to your veterinarian if you have a concern about your pet's symptoms or health.
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Canine Heartworms

The heartworm looks like a long white worm and lives in a dog's heart. It can also live in the blood vessels near the heart and lungs.

Baby Heartworms:

Adult Heartworms:

Heartworms are easily preventable but fatal if left untreated. The treatment can cause serious side effects.


Mosquitoes spread heartworms.

When a mosquito bites an infected dog, it ingests immature heartworms, which mature inside the mosquito. If that same mosquito bites your dog, your dog will get infected.


A lot of damage can occur before you notice any signs. These signs include:

If the disease has reached a critical stage, signs include:

At this point, damage to major organs is severe, treatment is complex, and the chance of full recovery is low.


To diagnose your dog with heartworms, your veterinarian will perform the following:

Based on this information and your dog's medical history, your veterinarian will diagnose your dog.


If you catch heartworms early enough, there is an excellent chance for treatment to be successful.

Baby Heartworms: Heartworm preventives will kill baby heartworms. In most cases, your veterinarian will admit your dog to the hospital for observation and then do another blood test to ensure the heartworms are gone.

Adult Heartworms: If your dog has adult worms, the baby worms must be treated first. Your veterinarian will recommend 1 to 3 months of preventive treatment before treating the adult worms.

Once the baby worms are gone, your veterinarian will most likely prescribe three doses of ImmiticideTM.

After treatment, you must ensure your dog has complete rest to prevent lung damage from the decomposing worms. Avoid exercise for at least a month, and gradually return to regular activity.

Severe heartworm cases may require surgical removal of the worms.


If your dog was treated for heartworms, they could get the disease again if you are not careful to follow a monthly preventive plan.

Most veterinarians recommend:


If you catch the heartworms early, there is an excellent prognosis. Depending on the number of worms and stage of infection, life-threatening complications may arise from both the disease and treatment.  

Medically Reviewed by Sara Ochoa, DVM

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