Why dogs and cats need heartworm protection

Heartworm – you’ve probably heard the term, but what’s it all about, exactly? And why is prevention so important?

What is heartworm disease?

Heartworm disease is a serious (and potentially fatal) condition caused by a microscopic organism called Dirofilaria immitis.1 The organism eventually matures into foot-long worms that inhabit the heart, lungs, and blood vessels of an infected animal. Left untreated, it can result in significant damage to the lungs and other organs, including heart failure.2

Heartworm disease is transmitted from animal to animal through mosquito bites. Adult heartworms in an infected animal, such as a dog, fox, coyote, or wolf, produce microscopic baby worms called microfilaria.2 A mosquito that bites an infected animal picks up these microfilaria. The microfilaria begin to mature within the mosquito. The mosquito then bites another animal and passes these older microfilaria onto another animal, where they complete their development, and the cycle continues.2

Is your dog or cat at risk of heartworm disease?

Since heartworms are spread by mosquitos, the more time a pet spends outside, the greater the chance of exposure.1 But, mosquitos can come inside, too, and heartworm disease has been diagnosed in pets in all 50 U.S. states, so every pet faces the risk.1

What are the signs of heartworm disease in dogs and cats?

Dogs infected with heartworms may start out with mild to no symptoms. As the condition progresses, the dog may develop a cough, lose their appetite (and lose weight), and become less active and easily fatigued.2

The disease can be trickier to spot in cats, and infection rates tend to be lower because cats aren’t heartworms’ typical hosts. Typically, only one to three worms survive in cats to the adult stage.1 But heartworms can still mean trouble. Infected cats can develop a cough or have difficulty breathing, and they may become lethargic and lose their appetite.1

The effects of heartworms on both dogs and cats can be significant – even deadly – so consult your veterinarian at any sign of trouble.

Protect your pet with year-round heartworm preventative medication

As is often the case, the best “treatment” is prevention. Heartworm disease can be serious and scary, so the best way to deal with it is to prevent it from happening in the first place.

It only takes a few minutes each month to administer preventative medication to your pet. Products such as SENTINEL® Spectrum® Chews (milbemycin oxime/lufenuron/praziquantel), SENTINEL® Flavor Tabs® (milbemycin oxime/lufenuron), and Tri-Heart® Plus Chewable Tablets (ivermectin/ pyrantel) offer proven heartworm protection for dogs. BRAVECTO® PLUS (fluralaner and moxidectin topical solution) for Cats can help keep your cat free from heartworm disease in addition to fleas and ticks.

It’s essential to administer preventative medication consistently all year. Mosquito species are constantly changing and adapting to colder climates and have the ability to overwinter indoors.2 So instead of guessing when your pet is at the highest risk, be safe and give your pet a preventative year-round.

Get your pet screened annually for heartworm

Getting your pet tested for heartworms during their annual veterinary checkup is vital for their health and protection. It takes about six months for a heartworm infection to be recognized and detected even with routine testing, given the lifecycle of heartworms.3 By getting a heartworm test from your veterinarian on a regular basis, you can keep your pet healthy with early detection and treatment, potentially saving their life.

If heartworms happen

If your pet shows signs of heartworms, or a heartworm infection (coughing, distended abdomen, weight loss, difficulty breathing, and/or exercise intolerance), act fast. Consult your veterinarian, who will likely perform blood tests to confirm the presence of heartworms.4 Radiographs or an ultrasound may also be performed to help your veterinarian understand the extent of the disease.

If heartworms are confirmed, medications are administered to kill the heartworms. Exercise restriction is very important during treatment and for at least 6-8 weeks post-treatment to minimize the risk of complications.5

Treating heartworm is a big deal, but with help from your veterinarian, it can be managed. Prevention, however, is NOT a big deal, so make sure your pets get the protection she needs.


  1. Atkins, Clarke E. Heartworm Disease in Dogs, Cats, and Ferrets. Merck Manual Veterinary Manual. https://www.merckvetmanual.com/circulatory-system/heartworm-disease/heartworm-disease-in-dogs,-cats,-and-ferrets
  2. American Heartworm Society. https://www.heartwormsociety.org/pet-owner-resources/heartworm-basics
  3. Heartworm Prevention for Dogs. American Heartworm Society https://www.heartwormsociety.org/pet-owner-resources/heartworm-prevention-for-dogs
  4. Keep the Worms Out of Your Pet’s Heart! The Facts about Heartworm Disease. U.S. Food & Drug Administration. https://www.fda.gov/animal-veterinary/animal-health-literacy/keep-worms-out-your-pets-heart-facts-about-heartworm-disease
  5. Heartworm Guidelines. American Heartworm Society. https://www.heartwormsociety.org/veterinary-resources/american-heartworm-society-guidelines


TRI-HEART® Plus (ivermectin/pyrantel). Keep out of reach of children. In case of ingestion by humans, clients are advised to contact a physician immediately. Infected dogs must be treated to remove adult heartworms and microfilariae before initiating a program with Tri-Heart® Plus chewable tablets. 1.1% of administered doses to dogs resulted in vomiting or diarrhea within 24 hours. Depression/lethargy, anorexia, mydriasis, ataxia, staggering, convulsions and hypersalivation were other reported adverse reactions. See package insert for full information regarding contraindications, warnings, and precautions.

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.

BRAVECTO® PLUS (fluralaner and moxidectin topical solution) for Cats: The most commonly reported adverse reactions include vomiting, hair loss, itching, diarrhea, lethargy, dry skin, elevated ALT, and hypersalivation. BRAVECTO® PLUS has not been shown to be effective for 2 months in kittens less than 6 months of age. Use with caution in cats that are heartworm positive. The effectiveness of BRAVECTO® PLUS to prevent heartworm disease after bathing or water immersion has not been evaluated.

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