Comparison Chart: Heartworm Prevention Medicine For Dogs

Key Takeaways

• Heartworm disease is transmitted by mosquitoes and can cause serious damage to a dog’s heart, lungs, and blood vessels, making prevention an important part of routine care.
• Veterinarians recommend year-round heartworm prevention and annual heartworm testing for dogs, regardless of climate, lifestyle, or time spent outdoors.
• Heartworm preventives are available as monthly chewables, topical treatments, and long-acting injections, with some products also protecting against fleas, ticks, and intestinal parasites.
• All heartworm prevention products require a veterinary prescription and a current negative heartworm test to help ensure they are used safely and appropriately.
• Consistent heartworm prevention is generally easier and less expensive than treating an existing infection, which can require extensive veterinary treatment and months of restricted activity.

---

Heartworm Prevention

If you've got a dog, heartworm prevention is one of the most important things you can do for their health. Heartworm disease is caused by a parasite spread through mosquito bites, and left unchecked, it can seriously damage your dog's heart, lungs, and blood vessels.

Today's heartworm preventives come in a few different forms: monthly chewable tablets, topical treatments, and long-acting injections your vet administers. Most contain ivermectin, milbemycin oxime, moxidectin, or selamectin. These are active ingredients that clear out heartworm larvae before they have a chance to mature into adult worms. Many of these products also protect against fleas, ticks, or intestinal worms, so it's worth comparing your options with your veterinarian to find the best fit for your dog.

Below, we break down the most common heartworm prevention products for dogs so you can see exactly what each one covers.

Why Year-Round Prevention Matters

You might assume heartworm prevention is only necessary during mosquito season, especially if you live somewhere with cold winters. That's not what veterinarians recommend. The American Heartworm Society follows a simple standard it calls “Think 12”: test your dog for heartworm every 12 months, and give them a preventive 12 months a year, no matter where you live.

American Heartworm Society: “Get your pet tested every 12 months for heartworm and give your pet heartworm preventive 12 months a year.”

Companion Animal Parasite Council: “All dogs, regardless of their lifestyle, should be on year-round heartworm prevention.”

Why does this matter so much? Mosquitoes get indoors more easily than you'd think, winters have grown milder and less predictable, and even one missed month leaves your dog exposed. Giving your dog their preventive every month, all year long, is simply the safest way to protect them, regardless of your climate or how much time your dog spends outside.

Is Heartworm Prevention a Prescription Medication?

Yes, every product on this list requires a prescription from your veterinarian. Federal law restricts these medications to use by, or on the order of, a licensed vet, and for good reason: your dog needs a current negative heartworm test before starting or renewing a preventive. Giving these medications to a dog that already has heartworms can trigger a dangerous reaction, so this step matters. Talk to your vet about which product, dosage, and testing schedule makes sense for your dog.

Comparison Chart: Heartworm Prevention Products for Dogs

Here's how the most common heartworm preventives for dogs stack up against each other:

Dog Products/ Manufacturer/ Administor	Heartworms	Hookworms	Roundworms	Whipworms	Tapeworms	Fleas	Ticks	Earlist Age	Active Ingredient
Advantage Multi / Elanco / Topical	yes	yes	yes	yes	__	yes (and mange)	__	7 weeks (and 3lbs)	Imidacloprid + Moxidectin
Heartgard Plus / BI / Chewable	yes	yes	yes	__	__	__	__	6 weeks	Ivermectin + Pyrantel
Interceptor / Elanco / Flavor Tab	yes	yes	yes	yes	__	__	__	4 weeks (and 2lbs)	Milbemycin Oxime
Interceptor Plus / Elanco / Chewable	yes	yes	yes	yes	yes	__	__	6 weeks	Milbemycin Oxime + Praziquantel
Iverhart Max / Virbac / Chewable	yes	yes	yes	__	yes	__	__	8 weeks	Ivermectin + Pyrantel Pamoate + Praziquantel
Iverhart Plus / Virbac / Chewable	yes	yes	yes	__	__	__	__	6 weeks	Ivermectin + Pryrantel
Sentinel Flavor Tabs / Merck / Flavor Tab	yes	yes	yes	yes	__	yes	__	4 weeks (and 2lbs)	Milbemycin Oxime + Lufenuron
Sentinel Spectrum / Merck / Chewable	yes	yes	yes	yes	yes	yes	__	6 weeks	Milbemycin Oxime + Lufenuron + Praziquantel
Trifexis / Elanco / Chewable	yes	yes	yes	yes	__	yes	__	8 weeks (and 5lbs)	Spinosad + Milbemycin Oxime
Tri-Heart Plus / Merck / Chewable	yes	yes	yes	__	__	__	__	6 weeks	Ivermectin + Pyrantel

Looking for broader coverage? Newer combination chews like Simparica Trio, NexGard Plus, and Credelio Quattro combine heartworm prevention with flea, tick, and other parasite protection in a single monthly dose. Ask your vet whether one of these all-in-one options might be a better fit for your dog.

What Does Heartworm Treatment Cost Compared to Prevention?

Here's another reason to stay consistent: the math is on your side. Monthly heartworm prevention typically runs $5 to $25 a month. Call it $60 to $300 a year, depending on the product and your dog's size.

Treating an actual heartworm infection is a different story. Between diagnostics, hospitalization, the melarsomine injection series, and months of strict activity restriction, treatment typically costs $600 to $1,200 and can run past $3,000 to $6,000 in severe cases. By some estimates, treating heartworm costs roughly ten times what a year of prevention would have cost.

• Prevention: about $5–$25 a month (roughly $60–$300 a year)
• Treatment: $600–$1,200 on average, more in severe cases
• Beyond the dollars: months of crate rest, repeat vet visits, and a real risk of complications as the dead worms break down in your dog's bloodstream

Keeping up with monthly prevention is the easier — and far cheaper — path for you and your dog.

Frequently Asked Questions

Can heartworm prevention be given late?

A dose that's a few days late generally isn't a big deal, though it does open a small gap in your dog's protection. Get back on schedule as soon as you can, and call your vet if a dose is more than a couple of weeks overdue. They may want to time your next heartworm test around it.

What happens if I miss a dose?

Give the missed dose as soon as you remember, then get back to your regular monthly schedule. If it's been more than 6 to 8 weeks since the last dose, call your vet before restarting. They may want to run a heartworm test first, since giving a preventive to a dog that's since been infected can cause a dangerous reaction.

Do indoor dogs need heartworm prevention?

Yes. Mosquitoes — the only way heartworm spreads — get inside through doors, windows, and screens more often than you'd think. Vets recommend year-round prevention for every dog, regardless of how much time they spend outside.

Is heartworm preventable if my dog already has it?

No. Heartworm preventives stop new larvae from maturing into adult worms. They don't treat an existing infection, and they're not a substitute for treatment. If your dog tests positive, your vet will walk you through a separate treatment protocol, usually a series of melarsomine injections combined with strict activity restriction. Your dog will need a heartworm test before starting or restarting any preventive.

How is heartworm transmitted?

Only through a mosquito bite. A mosquito picks up microscopic larvae after biting an infected animal, the larvae mature inside the mosquito for about 10 to 14 days, and then the mosquito passes those infective larvae along the next time it bites a dog or cat. Heartworm can't spread directly from one dog to another.

Sources: American Heartworm Society (heartwormsociety.org), Companion Animal Parasite Council (capcvet.org), American Veterinary Medical Association (avma.org), manufacturer and FDA product labeling (DailyMed), and cost reporting from PetMD, GoodRx, Vetster, CareCredit, and MetLife Pet Insurance.

Whether for horse, livestock, or pet, Valley Vet Supply is your one-stop shop for trusted care. Explore more of our dog category at ValleyVet.com