Heartworm Preventative Comparison (Heartgard, Interceptor, Tri-Hart)

HeartComparisonsMeongsiljang Veterinary Advisory Board

We’ll compare the ingredients, protection coverage, and administration methods of the three leading heartworm preventatives for dogs—Heartgard, Interceptor, and Tri-Hart—to help you choose the right product for your pet.

What Are Heartworm Preventatives?

Comparison of Three Heartworm Preventatives Thumbnail

Heartworm preventatives are deworming medications that eliminate heartworm larvae before they mature into adult worms after a mosquito bite. The most important thing is to administer the medication consistently on a set date every month. Skipping even one month can allow the larvae to develop into adults and establish themselves in the heart and pulmonary blood vessels. Heartgard, Interceptor, and Tri-Hart are the three most commonly used brands in Korea, and since their active ingredients and preventive coverage vary slightly, it’s important to choose the one that best suits your pet’s individual needs.

Why Is Comparison Necessary?

All three products prevent heartworms, but they differ in the additional types of parasites they protect against. Heartgard Plus covers roundworms and hookworms. Interceptor Plus protects against heartworm larvae, as well as whipworms, tapeworms, roundworms, and hookworms. Tri-Heart Plus offers a similar spectrum to Heartgard, including efficacy against roundworms and hookworms. Since Interceptor provides broader coverage by including whipworms and tapeworms, it may be more advantageous for multi-dog households or dogs that go on frequent walks and have high exposure to soil-borne parasites. However, if your dog has allergies or belongs to a specific breed, you should carefully review the active ingredients.

Heartgard, Interceptor, and Tri-Hart at a Glance

Item	Heartgard Plus	Interceptor Plus	TriHeart Plus
Active ingredient	Ivermectin + Pyrantel	Milbemycin oxime + Praziquantel	Ivermectin + Pyrantel
Heartworm prevention	True	True	True
Roundworm prevention	True	True	True
Hookworm prevention	True	True	True
Whipworm prevention	False	True	False
Tapeworm prevention	False	True	False
Formulation	Chewable jerky-type	Chewable jerky-type	Chewable jerky-type
Dosing schedule	Once a month	Once a month	Once a month

Ingredients and prevention scope are based on the manufacturer's official information; actual prescription is decided after consultation with a veterinarian

Heartgard Plus Features

Heartgard Plus is a heartworm preventive medication whose main active ingredient is ivermectin. Ivermectin eliminates the larval stages of heartworms that enter the body through mosquito bites, thereby preventing the infection from establishing itself. The low-profile chewable tablet is generally well accepted by dogs, who tend to eat it like a treat. The addition of pyrantel provides protection against heartworm larvae, roundworms, and hookworms, but it does not cover whipworms. Because certain breeds, such as Collies and Shetland Sheepdogs, may carry a genetic mutation (MDR1/ABCB1) that increases their sensitivity to ivermectin, genetic testing and consultation with a veterinarian are essential before administering this medication.

Close-up of heartworm preventive medication for small-breed dogs

Interceptor Plus Features

Interceptor Plus is a combination of milbemycin oxime and praziquantel, offering the major advantage of preventing not only heartworm but also whipworms and tapeworms in a single dose. It is particularly beneficial for dogs that go on frequent outdoor walks and have high exposure to soil-borne parasites. Although the milbemycin class has more accumulated safety data in Collie-type breeds, you should still consult your veterinarian before starting treatment.

Check Before Administration

Administering heartworm preventatives to a dog that is already infected with adult worms can cause fatal side effects. Therefore, it is essential to perform a heartworm antigen test before starting prevention for the first time, and again if treatment has been interrupted for more than six months. Since the dosage is determined by body weight, please measure your pet’s weight accurately and administer the specific formulation prescribed by your veterinarian.

Tri-Hart Plus Features

Tri-Hart Plus uses the same active ingredients as Heartgard Plus (ivermectin and pyrantel). Its prevention spectrum is nearly identical to Heartgard, with the advantage of being relatively more affordable. It can be a reasonable choice for pet owners who face significant long-term medication costs, such as those in multi-dog households. However, since it contains the same class of ingredients as Heartgard, the same precautions apply to Collie-type breeds.

A puppy sitting patiently while taking heartworm medication

Selection Criteria for Your Dog

- For dogs that go on frequent walks and are often exposed to grassy areas, Interceptor Plus is a better choice because it protects against whipworms and tapeworms as well. - For dogs that you’d like to give medication to easily, as if it were a treat, Heartgard Plus is a safe and reliable option, with proven palatability. - For multi-dog households or when long-term treatment is a financial concern, Tri-Hart Plus is a more economical choice, offering the same active ingredients at a lower price. - For specific breeds such as Collies and Shetland Sheepdogs, you must always have your dog tested for drug-sensitivity genes and obtain a prescription from your veterinarian before using any product.

Precautions by Breed and Health Status

Certain breeds, such as Collies, Shetland Sheepdogs, Old English Sheepdogs, and Australian Shepherds, may carry a genetic mutation that increases drug sensitivity, making them particularly susceptible to adverse reactions to ivermectin. For dogs with liver or kidney disease, senior dogs aged seven years or older, and those that are pregnant or nursing, it is essential to consult your veterinarian before switching products or starting a new regimen. Your vet will determine the appropriate dosage and schedule based on your dog’s weight and overall health status.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Should I still give my pet heartworm medication during the winter?

The American veterinary guidelines recommend year-round administration. As winters in Korea are becoming milder, mosquito activity periods are lengthening, making monthly year-round administration the safest approach.

Can I switch from Heartgard to Interceptor?

Yes, switching is possible. However, before making the change, consult your veterinarian to reconfirm the weight-based dosage and administration interval, and coordinate the schedule to avoid any gaps in preventive coverage.

Should I give the medication again if my pet vomits it up?

If your pet vomited right after taking the medication, it may not have absorbed enough of the drug. Whether to administer another dose or wait until the next scheduled dose depends on when the vomiting occurred and your pet’s current condition. Rather than giving the same dose again on your own, it’s safest to **contact your veterinarian first for guidance**.

Can cats take the same medication?

No, that’s not safe. Heartworm preventatives designed for dogs should never be used on cats. Cats require their own specific products (such as Revolution for Cats), which must be prescribed separately by a veterinarian.

Should I just pick the cheapest product based on price alone?

Rather than choosing based on price alone, consider your pet’s living environment, breed, and health status. If your pet is frequently exposed to parasites, a broad-spectrum product is recommended; for certain breeds, ingredient safety should be the top priority.

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References

[1] American Heartworm Society, Current Canine Guidelines for the Prevention, Diagnosis, and Management of Heartworm (Dirofilaria immitis) Infection in Dogs, 2020

[2] Handbook of Veterinary Pharmacology, Drugs for Heartworm Prevention and Therapy

[3] Textbook of Respiratory Disease in Dogs and Cats, Heartworm Disease Chapter