PetMD Editorial
Written by:
PetMD Editorial
Published: November 7, 2012

Drug Info

  • Common Name: Heartgard®, Ivermec®
  • Drug Type: Anti-parasitic
  • Used For: Prevention and treatment of heartworms
  • Species: Dogs, Cats
  • Administered: Flavored chew, tablet

General Description

Heartgard® is used for the treatment and prevention of heartworms, and is also effective against roundworms and hookworms. It is also an effective treatment against some other parasites, including ear mites. It is a beef-flavored chew or tablet that is given once a month. Some people believe that heartworm medication should only be given during the warm months of the year, but the medication only works on parasites your pet has been exposed to in the preceding month, so the American Heartworm Society recommends that heartworm prevention be used year round.

You can start giving your pet Heartgard® at as young as 6 weeks of age.

How It Works

Heartgard® works by interfering with the central nervous system of the heartworm larva. It is not effective against the adult form of the worm, but is often given to heartworm-infected dogs to prevent further growth. If your pet tests positive for heartworms, your veterinarian will likely use another drug, Immiticide®, to treat the adults.

Storage Information

Store at room temperature and protect from light. Keep sealed in foil package until use.

Missed Dose?

Give the dose as soon as possible. If it is almost time for the next dose or you have missed many doses, skip the missed ones and continue with the regular monthly schedule. Do not give the pet two doses at once. Notify your veterinarian that you missed a dose.

Side Effects and Drug Reactions

Heartgard® is safe to use in pregnant and lactating pets.

Heartgard® may result in these side effects:

  • Depression/lethargy
  • Vomiting
  • Anorexia
  • Diarrhea
  • Dilation of the pupils
  • Staggering
  • Convulsions
  • Drooling

Studies have shown that the Collie breed of dog may be more sensitive to elevated levels (16 times the recommended dose) of Ivermectin and more likely to have adverse reactions. However, at 10 times the normal dose of Heartgard®, no adverse effects were found in susceptible Collies, and Heartgard® is considered very safe at the recommended dose. If you are a concerned Collie owner, discuss the safety of Ivermectin with your veterinarian.

Ivermectin may react with a flea prevention medication Comfortis®, resulting in an Ivermectin toxicity in your pet. Discuss with your veterinarian and use caution if considering using these drugs concurrently.

Help us make PetMD better

Was this article helpful?

Related Articles

Connect with a Vet

Subscribe to PetMD's Newsletter

Get practical pet health tips, articles, and insights from our veterinary community delivered weekly to your inbox.