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Metairie Small Animal Hospital (MSAH)

National Heartworm Awareness Month: Preventing Heartworm in Dogs

Veterinarians with a Golden Retriever

Heartworm disease is potentially fatal to dogs, caused by foot-long worms that live in their heart, lungs, and blood vessels, causing severe distress to their organs. It affects dogs the most, as they are natural hosts for heartworms meaning they are the ideal environment for heartworms to mature into adults, mate, and reproduce. When left untreated, dogs can have a burden of several hundred worms at a time, causing lasting damage to their heart, lungs, and arteries. The damage can lead to a shorter lifespan and a poor quality of life, even if treatment is successful. As April is National Heartworm Awareness Month, we wanted to ensure you're equipped with what you need to prevent this potentially very harmful disease in your canine companion.  

Dog Heartworm Symptoms

The bite of an infected mosquito causes heartworm, making dogs prone to it simply from enjoying the outside world the AVMA details how heartworm is transmitted. In the early stages of heartworm disease, dogs may exhibit few to no symptoms. As the infection grows, symptoms will develop.

Symptoms of heartworm disease in dogs include:

  • Mild persistent cough

  • Fatigue following even moderate activity or exercise

  • Decreased appetite

  • Weight loss

  • Swollen belly

  • Labored breathing

  • Pale gums 

Dog Heartworm Prevention

Heartworm prevention medications come in a few different forms, including chewable pills, topicals, and injectable medications. These options make it easy to administer the medication even if your dog doesn’t do well with ingesting medicine. Heartworm medication is available only by prescription through your veterinarian, with some also protecting against other types of parasites, including fleas, hookworms and roundworms. Discuss heartworm preventive medications with your veterinarian to determine the best option for your dog.

The American Heartworm Society recommends monthly administration of heartworm preventive medication to give your dog the best chance of avoiding these parasites. Your dog needs it year-round, as it works by killing immature heartworms in an already-infected dog and preventing them from developing into adult worms. Some dog owners attempt medication-free strategies, but natural prevention does not exist since it’s nearly impossible to isolate a dog from mosquitoes 100% of the time. The American Heartworm Society also offers incidence maps so dog owners can understand the nationwide impact and where heartworm is most prevalent. 

Heartworm Testing

Due to the severity of heartworm, all dogs should be tested annually as part of their routine preventative care. Puppies under seven months old can begin heartworm medication without a heartworm test since it takes at least six months for a dog to test positive after being infected. We should give adult dogs over seven months a heartworm test before starting preventive medication, along with dogs who stopped taking heartworm medication for some time but intend to restart.

Even if your dog is on a monthly preventative, you should still have them tested annually. While heartworm medications are highly-effective, dogs can still become infected with heartworm disease. This is especially true if a dose is missed, administered late, not appropriately absorbed, or if they vomited shortly after taking it. Without a test, a dog’s owner won’t realize they’re suffering from heartworm until it’s become relatively advanced.


Contact us if you would like to learn more about heartworm prevention to ensure your dog maintains optimal wellness and excellent quality of life.