HomeResource CenterDoes My Dog Need Heartworm Prevention

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Does My Dog Need Heartworm Prevention: 13 Myths and Facts

Written by

Tracy Isenberg, LVT

As a pet parent, you may be wondering if your pup needs heartworm disease prevention. Or, what heartworm disease in dogs is.

The reality is, heartworm infection can lead to major health concerns and even death. And, according to the American Heartworm Society, 1 in every 100 dogs gets heartworm disease.

Don't worry, there are ways pet parents can prevent heartworms. And, if your pet is unfortunately infected with heartworm disease, there are treatment options that can help restore their health.

In this article, we debunk some common myths about heartworm disease in dogs. Plus, how you can protect your dog from heartworm infections.

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Myth #1: Heartworm disease isn't a big deal.#

Heartworm disease isn't a big deal

Fact: Heartworm disease can lead to serious health problems.

Heartworm infection is a severe disease in dogs. That's why preventing heartworm disease with monthly prevention is so important.

Heartworm disease in dogs can lead to health problems like:

  • Heartworm-associated respiratory disease
  • Severe lung disease
  • Heart failure
  • Organ damage
  • Death

Myth #2: Heartworm prevention medication kills all heartworms.

Fact: Heartworm preventatives do not kill adult heartworms.

But, they do prevent heartworm larvae from developing into adult heartworms. Heartworm prevention stops the growth and development of heartworm larvae in an infected dog. That's why prevention medication is important to keep your pet heartworm free.

Here's a quick look at how the heartworm life cycle works. All it takes is one mosquito bite:

1. A mosquito bites an infected animal.

When a mosquito feeds on an animal infected with heartworm, infective larvae pass from the animal to the mosquito through their blood. The infected mosquito then bites other animals and continues to spread the disease.

2. An infected mosquito spreads the disease.

When an infected mosquito bites your dog, microscopic worms spread to your dog's blood vessels. At this stage, your dog may show few or no symptoms. If you use preventative medications, the early stage larvae will not continue to develop.

3. Infective larvae grow into adult heartworms. 

If a dog is not taking heartworm preventative medications, these early stage larvae can mature into adult worms. As they grow, they migrate to other areas of your dog's blood and into their heart and lungs. At this stage, your dog may have mild symptoms like fatigue and nausea.

4. Adult heartworms reproduce and cause serious health problems.

When a heartworm develops in your dog's heart and lungs, they are able to reproduce. Adult heartworms can live for up to seven years inside your dog's body.

As heartworms multiply and grow, your dog may experience serious health issues. Large groups of heartworms take up space in your pet’s organs. This makes them difficult to remove, and damages your pet’s organs.

Myth #3: You don't need a prescription to start heartworm prevention.#

You don't need a prescription to start heartworm prevention

Fact: Heartworm prevention medication requires a prescription from a vet.#

To start heartworm preventatives, you need a prescription from your vet. To get a prescription, visit a doctor of veterinary medicine for a check-up and heartworm test.

Every year, your pet will need a heartworm test before starting heartworm prevention again. If your pet tests negative for heartworm disease, they’ll be eligible to start prevention medication.

A heartworm positive dog is not eligible for prevention. If your pet tests positive, your vet will outline your pup's heartworm treatment plan.

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Myth #4: Heartworm tests aren't important.#

Fact: All dogs need annual heartworm tests.

To receive a prescription for heartworm meds, your dog needs a heartworm test. And, annual heartworm tests help identify heartworm disease in an infected animal before it becomes a serious problem.

The most common way to test for heartworms is through a heartworm antigen test. This blood test only detects heartworm proteins from adult female heartworms.

An antigen test won't detect circulating heartworm antigen in your dog's bloodstream until around seven months after infection. That's why annual tests are important to catching the disease in its early stages.

Myth #5: Year-round prevention isn't necessary.

Year-round prevention isn't necessary

Fact: Your pup needs year-round prevention against heartworm disease.

Heartworm disease spreads through infected mosquitoes — which are more abundant in the warmer months. But, as the world continues to get warmer, pet parents should consider using heartworm prevention year-round.

Plus, heartworm disease occurs in all 50 states, regardless of climate. And, mosquitoes can live indoors for weeks.

If an infected female lays eggs in your home, you may get stuck with a series of infected mosquito generations in your home. That's why pet parents should not consider skipping heartworm prevention, even in colder months.


The American Heartworm Society recommends that pet owners use the "think 12" method. This means pet parents should get their dog tested for heartworm infection every 12 months, and give their dog heartworm prevention 12 months a year.

Myth #6: Indoor pets don't need heartworm prevention.

Indoor pets don't need heartworm prevention

Fact: All dogs need heartworm prevention.

Whether your pet spends the majority of their time outdoors or rarely sees the light of day, they need heartworm prevention. Mosquitoes carrying heartworm disease can bite your dog indoors. That means even indoor pets aren't completely safe from heartworms.

Myth #7: All dogs with heartworm infections act sick.

Fact: Infected pets may show no signs of heartworm disease.

Unfortunately, most dogs infected with heartworm disease show no signs of illness until their infection is severe. That's why getting your dog tested for heartworm disease every 12 months and sticking to a monthly prevention plan are so important.

If your dog’s heartworm condition has progressed into a more serious issue, they may show symptoms of heartworm like:

  • A mild, persistent cough
  • Fatigue
  • Decreased appetite
  • Weight loss
  • Swollen abdomen
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Myth #8: Heartworm treatment is the same as heartworm prevention.

Fact: Heartworm treatment is for infected dogs. 

Heartworm prevention medications stop the spread of infection. Treatment is for dogs already infected with heartworm disease.

The best way to prevent heartworm in dogs is by using monthly heartworm medication. And, pet parents should use heartworm medications year-round.

Myth #9: Heartworm prevention is expensive.#

Fact: Not all heartworm medication is pricey.

There are plenty of affordable options for heartworm preventatives out there for pet parents to explore. The most common forms of prevention include chews, flavor tablets, topicals, and injections.

Some heartworm medications can protect your pet from other parasites like:

Talk to your vet about which prevention option is best for your pet.

Myth #10: It’s okay to skip a dose of heartworm medication.

Its okay to skip a dose of heartworm medication

Fact: Just one missed dose can put your pet at risk of infection.

Heartworm preventatives are effective at treating the development of infected larvae that may have entered your dog’s bloodstream during the 30 days prior to treatment. So, if a mosquito bites your dog outside of that 30-day window and they aren’t protected, they may get infected.

If pet parents don't keep up with heartworm medication, the larvae can develop and grow into adolescent heartworms. This means when you start heartworm preventatives again, the medication will no longer be effective and can harm your pet.

Myth #11: Adult heartworms cannot reproduce.

Fact: Adult heartworms can produce offspring.

Once an adolescent heartworm fully develops into an adult heartworm, they are able to reproduce and multiply. When adult heartworms multiply and reproduce in your dog's heart, lungs, and associated blood vessels, they can cause major health problems.

Myth #12: Heartworms do not infect other animals.

Heartworms do not infect other animals

Fact: Heartworm disease can infect cats, ferrets, and other animals.

Although dogs are the natural host for heartworms, heartworm disease can also affect other animals. And, there are heartworm medications out there that can protect other pets from the disease.

Signs of heartworm disease in cats and ferrets vary based on the severity of the infection. Cat and ferret parents should visit their vet every year for heartworm testing.

Myth #13: Heartworm infections can spread between infected dogs.

Heartworm infections can spread between infected dogs

Fact: Only mosquitoes can spread heartworm disease.

If an infected dog comes in contact with your pet, they will not spread the disease to your dog. The only way for heartworm disease to spread is if a mosquito bites the infected dog and then bites your dog.

Keeping your pet safe from serious, life-threatening disease is an important part of pet parenting. Sticking to a monthly heartworm disease prevention plan is the best way to prevent heartworm disease.


Meet Tracy Isenberg

Tracy Isenberg, LVT is a member of PetFriendly’s in-house vet team. Tracy has over 25 years of experience working in the pet space as a veterinarian technician. She received her degree from Omaha College of Health Careers. Tracy has two dogs, a Bernese Mountain Dog named Bruno and a Yellow Lab Mix named Libby.