Signs of heartworm disease in dogs

Learn which signs to look out for so you can recognize if your dog has heartworm disease and seek effective treatment sooner rather than later.

Risks of heartworm disease in dogs

Heartworms can live in an infected dog for 5-7 years, so they can produce severe damage in your dog’s heart and lungs over time.1 This damage can include:

  • Clogging and damage to the lining of the arteries leading from the heart to the lungs
  • Heart value malfunction
  • Liver and kidney dysfunction
  • Heart failure

The heartworm lifecycle

A dog’s insides provide an ideal environment for the transmitted heartworms to mature into adults, mate and produce offspring.


  • 1

    Dog has an active heartworm infection. Larvae are produced by adult worms and circulate in the blood – they can appear in the dog’s blood 6-9 months after infection. 

  • 2

    Mosquito bites the dog and ingests blood containing heartworm larvae. 

  • 3

    Infective larvae are contained in the saliva of the mosquito.

  • 4

    The infective larvae enter the bite wound from the mosquito.

  • 5

    Larvae move through the dog’s tissue, making their way to the dog’s heart and pulmonary arteries 70 days after infection.

  • 6

    The larvae make their way to the dog’s heart and pulmonary arteries 70 days after infection.

  • 7

    Larvae develop into adult heartworms and reside in the dog’s pulmonary arteries, or in heavy infections, the chambers of the heart. 

  • 8

    Adult heartworms produce microscopic larvae that are released into the bloodstream.

The story of Charlie: a heartworm-positive dog

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Interceptor Plus prevents heartworm disease and treats and controls adult roundworm, hookworm, whipworm, and tapeworm infections in dogs and puppies 6 weeks or older and 2 pounds or greater.

Important Safety Information

Treatment with fewer than 6 monthly doses after the last exposure to mosquitoes may not provide complete heartworm prevention. Prior to administration of Interceptor Plus, dogs should be tested for existing heartworm infections. The safety of Interceptor Plus has not been evaluated in dogs used for breeding or in lactating females. The following adverse reactions have been reported in dogs after administration of milbemycin oxime or praziquantel: vomiting, diarrhea, decreased activity, incoordination, weight loss, convulsions, weakness, and salivation. For complete safety information, please see Interceptor Plus product label or ask your veterinarian.

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