Heartworm Prevention for Dogs

Protecting your dog from heartworm disease is easy with one Interceptor® Plus (milbemycin oxime/praziquantel) chewable tablet, every 30 days, year-round. Interceptor Plus is a heartworm medicine for dogs. It works by killing heartworm larvae after an infected mosquito bites your dog, before the larvae mature and become adult heartworms (Dirofilaria immitis).


heartworm incidence map

Map © American Heartworm Society:1 This map shows heartworm incidence based on the average number of cases per reporting clinic. Some remote regions of the United States lack veterinary clinics, therefore, no cases are reported from these areas.

It’s important to protect your dog year-round

You love doing everything with your dog, so make sure you’re always ready for your next adventure with year-round heartworm prevention. The Companion Animal Parasite Council and the American Heartworm Society recommend year-round treatment with a broad-spectrum parasite control product without interruption, regardless of where you live.2,3

Why your dog needs a year-round heartworm disease preventative

Don’t assume that cold winter weather eliminates the threat of heartworm disease in dogs. Starting and stopping heartworm medicine based on seasonality can cause gaps in your dog’s protection and leave them vulnerable to infection. But you can reduce this risk by protecting your dog from heartworm disease year-round.

However, if your dog has less than year-round heartworm prevention, it’s important to administer Interceptor Plus for at least 6 months after your dog’s last exposure to mosquitoes. It can take up to 6 months or longer for the signs of heartworm infection to manifest in your dog, and some dogs may display no signs at all. So, talk to your veterinarian about administering Interceptor Plus monthly, all year long—even in winter or other times you don’t see mosquitoes.

How does a dog get heartworm disease?

Heartworm disease is a potentially deadly infection that starts with the bite of an infected mosquito. From there, the larvae penetrate into a dog’s tissue and migrate to the bloodstream before entering the heart and lungs.

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.4 This damage can include:

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

Heartworm disease signs for dogs can include:

  • Coughing
  • Exercise intolerance
  • Difficulty breathing
  • Enlarged liver
  • Death

However, your dog can have a heartworm infection but display no visible signs. That’s why your veterinarian should perform a yearly blood test as part of your dog’s routine health check to determine whether there’s a potential heartworm infection. Because if left untreated, heartworm disease can be deadly for your dog.3

View video transcript


How dogs get heartworms diagram

Dog with active heartworm infection. Microscopic larvae (microfilariae) are produced by adult worms and circulate in blood. Larvae appear in the dog’s blood ≈6-9 months after infection.

Mosquito bites an infected dog and ingests blood containing microscopic heartworm larvae.

Microscopic larvae develop within the mosquito and into the infective stage ≈2 weeks under ideal conditions.

Infective larvae are contained in the saliva of the mosquito.

The infective larvae enter the bite wound from the mosquito and migrate into the tissue of the dog.

Larvae migrate through tissue and mature to enter bloodstream, making their way to the dog’s heart and pulmonary arteries ≈70 days after infection.

Larvae develop into adult heartworms and reside in the pulmonary arteries. In heavy infections, adult worms may invade the chambers of the heart and cause symptoms including coughing, sluggishness and difficulty breathing, though some dogs may show no signs at all.

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

Heartworm prevention for dogs

Prevention is your best weapon to protect your dog from heartworm disease and can save you the trouble and expenses associated with treating an infected dog. Plus, the treatment may not be 100% effective1 and your dog could have serious health complications.

Two vital steps to prevent your dog from developing heartworm disease:

1) Annual heartworm testing
Ask your veterinarian about testing your dog annually for a heartworm infection. If the test comes back positive, your veterinarian will discuss treatment options for your dog.

2) Year-round heartworm prevention
Give your dog the year-round heartworm protection of Interceptor Plus. It’s as easy as one chewable tablet every month, and then you’re all set for year-round heartworm disease prevention. If your veterinarian prescribes less than year-round prevention, it’s important to administer Interceptor Plus each month for at least 6 months after your dog's last exposure to mosquitoes.

Learn more about Interceptor Plus