This tried-and-true classic heartworm preventive is a favorite of dog parents everywhere.
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Many dog parents are aware of the threat of heartworm disease and use a form of heartworm prevention like Heartgard Plus to protect their dogs. It might be time to have a talk with to your veterinarian if you're not already protecting your dog from common disease-causing parasites. The American Heartworm Society recommends heartworm prevention for all dogs in the United States all year long. Plus, the Companion Animal Parasite Council recommends broad-spectrum parasite control to prevent heartworms, intestinal parasites, fleas, and ticks for all dogs in North America.

Heartgard Plus protects dogs from heartworms, roundworms, and hookworms and is one of the most popular products on the market. It does not protect against fleas and ticks, but there are additional products that can be given with Heartgard to offer full-spectrum protection.

What Is Heartgard for Dogs?

Heartgard and Heartgard Plus are monthly chewable heartworm prevention medications manufactured by Boehringer Ingelheim (BI). Each chew is made from beef and can be given as a treat—most dogs really love the taste.

Heartgard contains ivermectin, a macrocyclic lactone antiparasitic drug effective at killing heartworm larvae. Heartgard Plus contains ivermectin as well as pyrantel, an anthelmintic (worm-killing) drug in the tetrahydropyrimidine class that kills roundworms and hookworms. Most vets recommend Heartgard Plus over regular Heartgard due to its additional parasite control. In addition, Heartgard Plus is more readily available and less expensive than regular Heartgard.

Is Heartgard Safe for All Dogs?

Heartgard and Heartgard Plus are considered safe for most dogs, including pregnant and breeding dogs, but there are some exceptions. Ivermectin is not recommended for use in puppies under six weeks of age, so Heartgard should be started at this age and no sooner.

Some collie-type dog breeds and mixes have a gene mutation that makes them sensitive to ivermectin. Commonly affected dog breeds include collies, shelties, border collies, and Australian shepherds. Heartgard and Heartgard Plus should be used with caution in these breeds—it's recommended that collie-type dogs be observed for at least eight hours after Heartgard administration. Sensitive dogs are more likely to experience adverse reactions like depression, ataxia, tremors, drooling, coma, and even death. Some vets will recommend using a different type of heartworm prevention for these dogs. However, there is a specific test for the mutant gene ABCB1-1Δ (formerly called MDR1).

What Are Potential Heartgard Side Effects in Dogs?

Most dogs on Heartgard and Heartgard Plus experience no side effects. In clinical trials, adverse effects were rare. Vomiting or diarrhea were the most frequently reported side effects and typically occurred within 24 hours of dosing. The following adverse reactions have been reported following the use of Heartgard and Heartgard Plus:

Contact your veterinarian if your dog experiences these or any other undesired effects from Heartgard or Heartgard Plus.

Heartgard Dosage

Heartgard and Heartgard Plus should be given orally once per month at the recommended minimum dose of six micrograms of ivermectin per kilogram and five milligrams of pyrantel per kilogram of body mass. For convenient dosing, Heartgard and Heartgard Plus are each available in three sizes based on weight range:

  • Blue: Up to 25 pounds
  • Green: 26 to 50 pounds
  • Brown: 51 to 100 pounds

Dogs over 100 pounds will get a brown dose plus another dose equivalent to their weight over 100 pounds. So for example, a 115-pound dog would get a brown and a blue dose, while a 140-pound dog would get a brown and a green dose each month.

Most dogs like the taste of Heartgard and will eat it as a treat. For picky dogs, the chew can be broken into pieces and mixed with food, but it's important to make sure the dog eats the entire dose. You may wish to hide the pill in a tasty treat or Pill Pocket. If you miss a monthly dose of Heartgard, give the next dose immediately and resume a monthly schedule. Contact your veterinarian if your dog misses two or more monthly doses—your dog might need a heartworm test in about six months (it takes this long for heartworm larvae to mature enough to show up on a test).

Heartgard Vs. Other Heartworm Medications

Introduced in 1987, Heartgard was the first monthly heartworm preventative available for dogs. Dogs previously needed daily pills to prevent heartworm disease, so Heartgard really was a game-changer. Similar heartworm prevention products have been introduced since then, but the name-recognition and longevity of Heartgard has made it one of the most popular heartworm preventives on the market.

When it comes time to choose the right heartworm prevention for your dog, you'll find that there are many different brands and generics available. Some products only protect against heartworm disease and intestinal parasites, while others contain additional ingredients to prevent fleas and ticks. The following are just a few alternative products available to prevent heartworm disease and other parasites:

  • Tri-Heart Plus is another brand-name monthly chewable that is made from ivermectin/pyrantel and is very similar to Heartgard Plus. Tri-Heart Plus is made by Merck. In addition, other forms of generic ivermectin like nuheart may be found in certain markets.
  • Interceptor Plus is made by Elanco and contains ​milbemycin oxime, another drug that kills heartworm larvae, roundworms, and hookworms. Interceptor Plus also contains praziquantel, which kills tapeworms (which are transmitted by fleas).
  • Sentinel Spectrum is a monthly chewable made by Merck that contains ​milbemycin oxime and praziquantel to kill heartworm larvae, hookworms, and roundworms. Sentinel Spectrum also contains lufenuron for flea control. Lufenuron sterilizes fleas so they can't lay eggs, but it won't actually kill fleas.
  • Revolution for Dogs is a monthly topical product made with selamectin. Revolution kills heartworm larvae, fleas, ear mites, sarcoptic mange, and American dog ticks.
  • Simparica Trio is a monthly chewable tablet made with moxidectin, sarolaner, and pyrantel pamoate. It kills heartworm larvae, fleas, hookworms, roundworms, and five species of tick.
  • Trifexis is a monthly chewable tablet containing milbemycin oxime and spinosad. Trifexis kills heartworm larvae, fleas, hookworm, roundworms, and whipworms.

Dogs on Heartgard Plus will need additional treatment to keep fleas and ticks away. The following products are often paired with Heartgard:

  • Nexgard: Also made by BI, Nexgard is a monthly chew made with afoxolaner. It kills fleas and four species of ticks.
  • Bravecto: Made by Merck with the active ingredient fluralaner, Bravecto is available as a chewable tablet or topical solution. It protects dogs from fleas and three species of ticks for 12 weeks. It offers protection against an additional tick species (lone star tick) for eight weeks.
  • Advantix/Advantage: Bayer (owned by Elanco) makes three topical parasite prevention products: K9 Advantix II (kills/repels fleas, ticks, and mosquitos), Advantage II (kills/repels fleas), and Advantage Multi (kills/repels fleas and kills heartworm larvae).
  • Seresto: Also made by Bayer (owned by Elanco), Seresto is a collar that repels and kills both fleas and ticks for eight months.
  • Frontline Plus: Made by BI, Frontline Plus is a topical product made with fipronil that kills fleas and ticks.

Phew, that's a lot of information! It can be tough to decide on the right products, so talk to your vet about the best options for your dog and your budget. 

How Much Does Heartgard Cost?

The cost of Heartgard Plus generally ranges from $5–$8 per dose depending on the tablet size, number of doses, and source of purchase. It comes in a pack of six or 12, but most veterinarians sell individual doses for growing puppies. Heartgard Plus can be purchased directly from your vet, from your vet's online pharmacy, or through an external online pharmacy with a valid prescription. Regular Heartgard (ivermectin but no pyrantel) is typically slightly more expensive despite containing only one drug.

Heartgard Plus costs less per dose when purchased in a 12-pack (compared to the six-pack or individual doses). Although the price may be even lower via online pharmacies, BI may only guarantee the product if it was purchased directly though your vet (in the clinic or via their online pharmacy). The satisfaction guarantee means that BI will cover some or all vet expenses should your dog develop heartworm disease, hookworms, or roundworms. However, your dog must have a history of negative heartworm and fecal test results. This is why it's best to follow your vet's recommendations for annual physical exams and tests.

Do I Need a Vet Prescription for Heartgard?

Yes, Heartgard Plus is only available with a valid prescription from a veterinarian. It may be purchased directly through your veterinarian's office or an online pharmacy with a valid prescription.

Heartgard Drug Interactions and Warnings

In clinical trials, Heartgard Plus was considered safe when used along with several common flea collars, shampoos and dips, anthelmintics (antiparasitic drugs), antibiotics, steroids, and vaccines.

Some drug interactions have either been reported or are potentially harmful to dogs, including concurrent use of benzodiazepines and ketamine. Be sure to tell your veterinarian about all other medications and supplements that you give to your dog.