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6 min read

What is the Safest Heartworm Prevention for Dogs

Written by

Tracy Isenberg, LVT

Pets are a key part of families. Giving them a long, happy life is important. One way to do this is by taking preventive measures when approaching your pet's overall health.

For certain diseases, prevention is the key to keeping pets healthy. For heartworm disease, this stands true. But, what is heartworm disease? And, what is the safest heartworm prevention for dogs?

In this article, we'll cover:

  • The reality of heartworm disease
  • What is heartworm prevention
  • What to look for in heartworm prevention
  • Types of heartworm medicines for dogs
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The reality of heartworm disease

The reality of heartworm disease

Heartworm infection is a life-threatening illness spread by mosquitoes. When an infected mosquito bites your dog, they spread heartworm larvae to your dog's bloodstream.

The larvae eventually grow in size and travel to your dog's heart and pulmonary artery. If left untreated, these parasites can grow up to a foot long.

As the heartworms in your dog's body grow and reproduce, they can cause severe health concerns in your dog's life. Infected dogs may have symptoms like:

  • Pale gums
  • Fatigue
  • Weight loss
  • Labored breathing
  • Sensitive stomach
  • Kidney failure

All it takes is one mosquito bite to put your pet's health at risk. That's why annual testing for heartworms and preventive medications are important in your dog's life.


Dogs diagnosed with heartworm infection are not eligible for prevention medications. Instead, a vet will recommend heartworm treatment to treat your dog's condition.

It's important for pet owners to stick to a monthly prevention plan. Staying consistent with prevention is the best way to keep your dog free of heartworm infection.

What is heartworm prevention

What is heartworm prevention

Heartworm prevention medication works retroactively to treat the development of heartworm infections. This means it works to prevent the growth of heartworm larvae in your dog's body.

Using heartworm preventatives is the best way to prevent heartworm disease in dogs. And, the best prevention products can also protect your pet from other internal parasites like hookworms and roundworms.

Heartworm medication comes in different forms:

  • Chewable tablets
  • Soft chews
  • Topical treatments
  • Injections

Topical treatments are applied monthly and are split into weight breaks. Injections are given by a veterinarian every 6 or 12 months.

If your pet uses a chewable tablet or other oral medication for heartworm, it typically comes in three weight breaks for smal;, medium, and large dogs. For extra large dogs, you may need to combine doses of heartworm preventives to cover your dog's weight.


Pet parents cannot buy pet meds for heartworm without a prescription from their veterinarian. To get a vet prescription, your dog will need a heartworm test.

The American Heartworm Society recommends taking your dog to a veterinarian for a heartworm test every 12 months. And, dogs should receive heartworm preventatives 12 months a year.

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What to look for in heartworm prevention medication

What to look for in heartworm prevention medication

When choosing prevention medication for your dog, there are important factors you should look for. The best heartworm prevention pet meds have the following 5 qualities.

1. Prevent heartworm larvae growth.#

The best heartworm prevention medication prevents heartworms from developing out of the larvae stage. These parasitic worms are harmless to your dog, as long as they do not develop into adult heartworms.

2. Cover hookworms and roundworms.

Consider choosing a heartworm medication that also treats internal parasites in your dog's body like hookworms and roundworms. These parasites can damage your dog's health and require more trips to the vet for treatment.

3. Made with safe and effective ingredients.#

The active ingredients in the heartworm medicine you choose should be vet-quality and FDA-approved.

The most common active ingredient in heartworm pet meds is ivermectin, but other prevention medications use ingredients such as:

  • Milbemycin oxime
  • Moxidectin
  • Selamectin
  • Pyrantel

4. Do not cause adverse reactions.

Most dogs should not have any allergic reactions or side effects to their heartworm medication. If your dog has an adverse reaction after taking heartworm drugs, visit your vet immediately for a dog check-up.

Some herding dog breeds and mixed breed dogs have a genetic mutilation called MDR1. The MDR1 gene causes sensitivity to ivermectin.

Some common breeds that are prone to the MDR1 gene include:

  • Australian Shepherd
  • Border Collie
  • Collie
  • German Shepherd
  • Old English Sheepdog
  • Shetland Sheepdog
  • Miniature American Shepherd
  • Skye Terrier
  • Mixed breeds that may have herding-breed heritage

No matter what breed of dog you have, talk to your veterinarian about the best option for heartworm prevention.

5. Delivered every month.#

Most heartworm preventatives come in packs of three or six. That means pet parents have to remember to give their dogs their treatment every month.

Look for a product that does the work for you by delivering your pet’s dose every month right when they need it.

Try Wags Advance for Dogs

Types of heartworm medications for dogs

ypes of heartworm medications for dogs

When it comes to the best heartworm medicine for dogs, there are plenty of options for dog owners on the market. Consider your pet's current health, needs, and other pet medications they are taking when choosing a heartworm preventative.

Heartgard® Plus

Heartgard uses a combination of active ingredients including ivermectin and pyrantel to treat heartworms, hookworms, and roundworms in dogs. Heartgard Plus is a soft chew that comes in 6- or 12-month supplies.

Tri-Heart® Plus

Tri-Heart Plus is a chewable tablet that comes in a 6-month supply. It has the same active ingredients as Heartgard Plus.

Advantage Multi®

Advantage Multi is a topical treatment that treats heartworms, hookworms, roundworms, whipworms, and ear mites in dogs. It also treats adult fleas on dogs, however, it does not prevent or kill ticks, mosquitoes, flea eggs, or flea larvae.

Simparica Trio

Simarica Trio is a chewable tablet that kills fleas, flea eggs, flea larvae, and ticks on dogs. It also prevents heartworms, hookworms, and roundworms. Like Advantage Multi, Simparica Trio does not repel fleas, ticks, or mosquitoes.

Complete care doesn’t stop at heartworm prevention. Keep your pet healthy with a flea and tick treatment that kills and repels all three stages of biting fleas and ticks.

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Frequently asked questions about heartworm prevention

It's important for pet parents to understand the ins and outs of prevention medication for dogs. Here are some frequently asked questions about heartworm prevention.

Is heartworm treatment the same as prevention?

No. Heartworm treatment is for dogs infected with heartworm disease. Heartworm prevention medication is for healthy dogs who are not heartworm-positive.

Are vet prescriptions necessary for heartworm meds?

Yes, you need a prescription from a vet to purchase Tri-Heart, Heartgard Plus, Heart Defense, or any other heartworm prevention.

What's the best way to prevent heartworms?

The best way to prevent heartworm infections is through monthly prevention. Keep your pet's safety top of mind and choose a preventative to keep your dog safe from disease.

Can an infected animal spread heartworm infection?

Heartworm spreads between animals by infected mosquitoes. If your dog carries the disease and comes in contact with other dogs and cats, they cannot spread the disease.

Can my dog get heartworm from cats or guinea pigs?

Heartworm infections cannot spread from cats or guinea pigs to dogs. But, pet owners with dogs and cats should also protect their cats from heartworm infections with routine testing.

What pet medications are available without a prescription?

There are plenty of pet medications you can get for your dog without a prescription from a vet. For example, you can purchase flea and tick protection without a vet's prescription.

Over-the-counter medications for allergies, pain relief, and anxiety are also available without a prescription from a veterinarian.

Try Wags Advance for Dogs

When it comes to keeping your dog in good health, there are many factors to consider. Cross heartworm prevention off your list by choosing a proven prevention method and sticking to it every month.


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.