Woman and man kissing their dog in between them

How to prevent heartworm disease

Heartworm in dogs can be treated, but prevention is best

The good news is that most dogs with heartworm disease can be successfully treated, usually with drugs that kill adult heartworms and their offspring.1 But heartworm treatment is a long and difficult process, so, like many other pet-related health issues, prevention is best. It’s safer, less expensive, and better for your pet!

Testing and prevention

Preventative medications are extremely effective and when given properly, on a regular basis, can prevent your pet from contracting heartworm disease. Still, even dogs on preventative medication should be tested regularly for heartworm — because if a dog is already infected with heartworms, giving him preventative medication may be harmful or deadly.2

One issue is that if a heartworm-positive dog doesn’t get tested before starting a preventative, she’ll remain infected.2 However, her owner probably won’t know until she gets sick enough to show symptoms. Immature heartworms remain undetected and pets may appear healthy.2 Dogs should be tested before they start heartworm preventatives.2 Heartworm preventatives do not kill adult heartworms in already infected dogs.2 Also, if microfilariae (infected heartworm larvae) are in the dog’s bloodstream, the preventative may kill the microfilariae suddenly, triggering a shock-like reaction — and possibly death — of the dog.2

And remember, year-round heartworm protection is only as good as your diligence in remembering to give your pet the prescribed medication.

Can I get heartworm from my pet?

Heartworms are transmitted by the bite of an infected mosquito.2 Pets can’t catch heartworm from each other, and you can’t catch it from them. Many heartworm preventive medicines, including SENTINEL® Spectrum® Chews and SENTINEL® Flavor Tabs® also provide effective protection against other internal parasites, including hookworms, roundworms, whipworms and tapeworms.3,4 This is just one more reason to talk to your veterinarian about regular parasite prevention for your dog.


  1. Heartworm. Companion Animal Parasite Council. https://capcvet.org/guidelines/heartworm/
  2. Keep the Worms Out of Your Pet’s Heart! The Facts about Heartworm Disease. FDA.gov. https://www.fda.gov/animal-veterinary/animal-health-literacy/keep-worms-out-your-pets-heart-facts-about-heartworm-disease
  3. Sentinel® Flavor tabs®. https://merckusa.cvpservice.com/product/view/1047561
  4. Sentinel® Spectrum® Chews. https://merckusa.cvpservice.com/product/basic/view/1047562

Important Safety Information:

SENTINEL® SPECTRUM® Chews (milbemycin oxime/lufenuron/praziquantel). Dogs should be tested for heartworm prior to use. Mild hypersensitivity reactions have been noted in some dogs carrying a high number of circulating microfilariae. Treatment with fewer than 6 monthly doses after the last exposure to mosquitoes may not provide complete heartworm prevention. For complete product information refer to the product insert.

SENTINEL® FLAVOR TABS® (milbemycin oxime/lufenuron). Dogs should be tested for heartworm prior to use. In a small percentage of treated dogs, digestive, neurologic, and skin side effects may occur. For complete product information refer to the product insert.

Want to share this article?

More like this