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Heartworm in Dogs & Puppies

05/06/2018 by Colleen Williams
May 6th, 2018 by Colleen Williams

Heartworms are parasites that cause infection of the cardiovascular system, especially in small animals. Although small, heartworms can cause severe internal damage to organs and should be treated immediately. As the weather warms up, heartworm infections are more common, as the parasites are spread by mosquitos. By learning how to recognize heartworm symptoms in dogs, you could save your pet’s life. Remember: heartworm can be found in all 50 states.

What causes heartworm?

The bite of an infected mosquito transmits the parasite, a roundworm called Dilofilaria immitis.  After a pet is bitten by an infected mosquito, the roundworm’s larvae enter the skin through the bite wound and emerge into the bloodstream.

Heartworms reproduce quickly and become adults within 6 months, reaching up to a foot in length. Mature heartworms may live 5 to 7 years inside an untreated dog; up to 250 heartworms can live in a single pet. The parasites live in the internal organs, namely the heart and lungs, and blood vessels.

Symptoms of heartworm

During the early states of infection, pets may be asymptomatic, showing no signs of heartworms. As the disease progresses, the following symptoms may appear:

  • Coughing
  • Exercise intolerance
  • Anemia (iron deficiency)
  • Hypertension (high blood pressure)
  • Difficulty breathing
  • Tachycardia (rapid heartbeat)
  • Fainting
  • Partial heart failure

Diagnosis & Treatment

heartworm awareness month

Your vet will run blood tests in order to check for heartworms. The earliest heartworms can be detected is 5 months after a dog has been bitten by an infected mosquito.

While the best treatment is prevention, animals can be exposed to the disease for a variety of reasons and need to be put on special therapies immediately. Heartworm treatment is expensive – it can run anywhere from $1,000 – $3,000 (whereas preventative monthly treatments can range from $5 to $20).

It also isn’t easy for the sick pet; you may need to visit the vet multiple times for bloodwork, x-rays, hospitalization, and a series of injections, and pet insurance can help off-set the costs of the diagnostics and treatment. While your dog is undergoing heartworm treatment, it’s essential to limit physical activity; as the medication kills the heartworms, they break up into tiny pieces, which can become lodged in the blood vessels and lead to congestive heart failure.

The American Heartworm Society
is very clear that alternative therapies claiming to be “natural” or “herbal” will not be effective or safe in the treatment of heartworm disease.


It’s is the best way to keep your pets healthy, so book an appointment with your vet to get tested, and then get the oral or topical medicines needed to prevent the disease. Expect to pay around $100 – $200 for a year’s worth of heartworm prevention.

If you live in an area where heartworms are rampant, it’s highly recommended to start prevention in puppies as young as 8 weeks old. Be aware, as your pet grows, the dose of medication must also be increased, as it is based on weight. These treatments must be administered exactly as directed, on schedule, or heartworm larvae could hatch and lead to infection.

Heartworm in Cats & Humans

Cats are resistant and atypical hosts for heartworms, but they can be infected. The symptoms are like those in dogs, however most cats do not have adult worms, they have a shorter life cycle for the parasite. Unfortunately, cats run the risk of misdiagnosis because it is rare; however heartworms can still cause organ damage and respiratory diseases.

Heartworms cannot be passed between pets and humans.

Remember: Test Annually

If a heartworm-positive dog is not tested before starting their preventive regimen, the dog will remain infected and the disease will progress. Preventive medicines do not kill heartworms and can trigger dangerous reactions and possible death. Test your dogs and cats every year at your annual vet visit.

Visit the American Heartworm Society for more resources and to get the facts about heartworm disease.

Beating heartworm is tough enough – with Healthy Paws, pet parents don’t have to choose between their pet and their wallet. By signing up for pet insurance when pets are young, ongoing treatments will be covered up to 90%. Find out more by getting a free quote.