Heartworm Prevention for Dogs: What It Costs and How to Choose

Heartworm prevention stops a parasite that lives in your dog's heart and lungs

Heartworm prevention is a monthly or yearly medication that keeps your dog from getting infected with heartworms — parasites transmitted by mosquitoes. Your dog needs this medication year-round in most of the United States, though some regions with freezing winters can stop during cold months. The medication does not treat an existing infection; it only prevents new ones. If your dog already has heartworms, a different (and more expensive) treatment is required.

You get heartworm prevention from your veterinarian, either as a prescription you fill at a pharmacy or as a product the vet dispenses directly. The cost varies widely depending on which medication you choose, your location, and your vet's pricing — anywhere from $100 to $300 per year is typical, though some options cost more.

Key Takeaways

• Heartworm prevention is a monthly or yearly medication prescribed by your veterinarian, and your dog needs it year-round in most U.S. regions.
• Monthly medications like Simparica Trio, Bravecto Plus, and NexGard Plus cost roughly $15 to $40 per dose, while yearly injections like ProHeart 6 run $150 to $300 upfront.
• Your vet must run a heartworm test before starting prevention to confirm your dog is not already infected.
• Prescription heartworm preventers are more reliable than over-the-counter products, and your vet can recommend which works best for your dog's age and health.

Monthly pills and topicals: the most common choice

Most dog owners use a monthly heartworm preventive, usually combined with flea and tick protection in a single dose. Simparica Trio (chewable tablet), Bravecto Plus (chewable tablet), and NexGard Plus (chewable tablet) are the most widely prescribed. Each covers heartworms, fleas, and ticks. A single dose costs roughly $15 to $40 depending on your dog's weight and your vet's pricing.

You give these once a month, every month, year-round. The cost over a year runs $180 to $480 for the medication alone. Some vets offer a discount if you buy a six-month or twelve-month supply upfront. Others allow you to fill the prescription at a human pharmacy or online pet pharmacy, which may be cheaper than buying directly from the vet — ask your vet whether they will write a prescription you can take elsewhere.

Topical preventives like Advantage II or Revolution Plus go on your dog's skin once a month. These tend to cost slightly less than tablets but work the same way. Some dogs do better with a topical if they spit out pills or have a sensitive stomach.

Yearly injections: one shot instead of twelve doses

ProHeart 6 is an injection your vet gives once a year that prevents heartworms for six months, then again at the six-month mark (so two shots per year, spaced six months apart). The upfront cost is typically $150 to $300 per injection, so roughly $300 to $600 per year. The advantage is that you do not have to remember a monthly dose, and some owners find it cheaper than buying twelve monthly pills.

ProHeart 6 does not cover fleas or ticks, so you will need a separate flea and tick prevention if you choose this route. Your vet injects it under the skin, and it takes about two weeks to reach full protection. This option works well for dogs whose owners struggle with monthly schedules or for dogs that refuse pills.

What your vet needs before prescribing

Before your vet will prescribe any heartworm prevention, your dog must have a heartworm test. This is a blood test that detects whether your dog already has heartworms. If your dog is infected, giving prevention will not treat the infection and may cause serious side effects. The test costs $25 to $50 at most vet clinics.

Your vet will also ask about your dog's age, weight, and any health conditions. Puppies under eight weeks old cannot start heartworm prevention yet. Pregnant or nursing dogs may need a different product. Dogs with certain liver or kidney problems may not be candidates for some medications. Your vet will recommend which prevention is safest for your individual dog.

If your dog has had heartworm prevention continuously for the past year, many vets will skip the annual test and prescribe based on your word that the dog is protected. Ask your vet about their policy — some require a test every year regardless.

Over-the-counter products versus prescription options

Pet stores and online retailers sell heartworm preventives without a prescription, usually labeled as "natural" or "herbal" options. These products are not regulated the same way prescription medications are, and there is no may provide they work. The FDA does not review them before they reach the market.

Prescription heartworm preventives like those listed above have been tested for safety and effectiveness. Your vet can tell you which one is right for your dog and monitor for any side effects. If you use an over-the-counter product and your dog gets heartworms, you will face a much more expensive treatment bill — typically $500 to $2,000 depending on how advanced the infection is.

Heartworm treatment if prevention fails

If your dog gets heartworms despite prevention (which is rare with prescription medications used correctly), treatment involves injections of a drug called melarsomine, given over several weeks. The cost ranges from $500 to $2,000, and your dog must be hospitalized or closely monitored during treatment. Some dogs have permanent heart damage even after successful treatment.

This is why prevention is far cheaper and safer than treating an infection. Missing doses or using an unreliable product puts your dog at real risk.

Frequently Asked Questions

Can I stop giving heartworm prevention in winter?

In most of the United States, heartworms are transmitted year-round because mosquitoes survive indoors and in warm microclimates. Your vet will tell you whether your region has a true off-season. In northern states where temperatures drop below freezing for weeks at a time, you may be able to stop from November through March, but most vets recommend year-round prevention to be safe.

What happens if I miss a dose?

If you miss a monthly dose by a week or two, give it as soon as you remember and resume your normal schedule. If you miss it by more than a few weeks, contact your vet — they may recommend a heartworm test before restarting. Consistency matters because the medication only protects against infections acquired during the month it covers.

Can I use heartworm prevention meant for a larger dog on my smaller dog?

No. Heartworm preventives are dosed by weight, and giving too much can cause side effects. If your dog is between sizes, your vet will recommend which dose is appropriate. Never split a pill or dose meant for a larger dog.

Do indoor dogs need heartworm prevention?

Yes. Mosquitoes can enter homes through doors and windows, and even dogs that rarely go outside can be bitten. Indoor dogs are actually at higher risk in some cases because owners assume they do not need protection. Your vet will recommend prevention regardless of whether your dog spends time outdoors.

Is there a heartworm prevention that also covers intestinal worms?

Some products cover multiple parasites. Simparica Trio, for example, covers heartworms, fleas, ticks, and some intestinal worms. Ask your vet which combination products are available and whether your dog needs coverage for intestinal parasites based on your region and lifestyle.