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Heartworm Treatment for Dogs

By the Dog Health Handbook team · Updated · Fact-checked against current veterinary references (see sources)

Key takeaways

  • Treatment follows the AHS protocol over about 5 months.
  • Three adulticide injections kill about 99% of worms.
  • Strict rest lasts until 6 to 8 weeks after the last injection.
  • About 1% of dogs die during treatment in recent studies.
  • Slow kill isn't recommended except as a last resort.

Table of Contents

Research Protocol Exercise restriction Side effects Severe disease Slow kill Cost After treatment FAQ Sources

Heartworm Quicklinks

Heartworm Symptoms How Dogs Get It Testing Treatment Prevention Other Worms

Heartworm treatment for dogs follows a protocol from the American Heartworm Society (AHS) that takes several months. First, a positive test is confirmed and the dog is stabilized if it's ill.1,2 The dog then gets a heartworm preventive and a 4-week course of a tetracycline-class antibiotic. Three injections of an arsenic-based adulticide follow: one on day 60 and two more about a month later, 24 hours apart.3 This is the only FDA-approved drug that kills adult heartworms.3,4 The three-injection protocol kills about 99% of worms.1 Strict rest is essential from diagnosis until 6 to 8 weeks after the last injection, because dying worms can block blood vessels in the lungs.1,3 A follow-up antigen test is done 9 months after the last injection.3 Treatment averages about $1,457 per dog, so prevention is far cheaper.5 "Slow kill" methods using only preventives are not recommended.1,6

Call your vet or an emergency clinic during treatment if your dog has:

  • Trouble breathing, coughing up blood, fever or collapse. These can be signs of a blood clot in the lungs, which usually appears 7 to 10 days after an injection.1,7
  • Loss of appetite or depression7
  • Severe pain or swelling at the injection site7,8

What the Research and Guidelines Say

  • High success. In a 2026 study of 283 dogs treated with the three-injection protocol, every dog retested after 6 months was negative, and 0.7% died during treatment.8
  • Affordable care is possible. Two low-cost Texas clinics treated 556 dogs for $225 to $614 each. 1.3% died, and 99% of those retested were negative.9
  • Guidelines often aren't followed. In a 2026 study of 679 US clinics, only 28% of dogs received all three injections.5
  • Antibiotic blocks spread. 2023 and 2026 studies found that when treated dogs got the tetracycline-class antibiotic with a preventive, larvae that mosquitoes picked up from them could not grow into adult worms in new dogs.10,11

The AHS Treatment Protocol

  • Diagnosis (day 0): confirm the positive test, start a heartworm preventive, a 28-day course of a tetracycline-class antibiotic and strict rest. Dogs with signs are stabilized and given a tapering steroid.3,1
  • Days 30 to 59: on day 30 the vet checks the antibiotic course is finished, then a waiting period of about a month follows3
  • Day 60: the first adulticide injection, with pain control, a steroid taper and rigid rest3
  • Days 90 and 91: the second and third injections, 24 hours apart3
  • Day 120: a test for microfilariae, then a gradual return to activity over 4 weeks3
  • About day 365: antigen and microfilaria tests, 9 months after the last injection3

The antibiotic targets Wolbachia, bacteria that live inside heartworms. Treating them "reduces pathology associated with dead heartworms and disrupts heartworm transmission."1

Exercise Restriction

AHS says "a pivotal factor in reducing the risk of thromboembolic complications is STRICT activity restriction." Dying worms break up and can block blood vessels in the lungs.1,7 Rest means "cage restriction, on-leash when taken outside to eliminate," from diagnosis until 6 to 8 weeks after the last injection.3 No running, jumping on furniture or playing with other dogs. Ask your vet about calming medicines if your dog struggles with confinement.9,12

Side Effects

  • Injection-site pain and swelling: in a 2026 study, 9.2% of dogs had soreness after the first injection and 2.1% after the third.8,7
  • Coughing as worms die. It can last several weeks in heavily infected dogs.8,7
  • Lung blood clots (thromboembolism): usually within 7 to 10 days of an injection, but possible up to 4 weeks after1
  • Antibiotic side effects: mainly vomiting and diarrhea. Studies report raised liver enzymes in up to 40% of dogs, usually without causing illness.1

Dead worms aren't passed in stool. Their fragments lodge in small lung vessels and are gradually "reabsorbed by the body."7

Severe Disease and Caval Syndrome

Dogs with heart failure or severe lung disease are stabilized first, which can take months.2,1 Dogs with caval syndrome need emergency surgery to remove worms from the heart, at a cost of about $3,000 to $6,000.13,14 Older dogs get the same protocol, which AHS recommends regardless of disease stage, and your vet will weigh their overall health and other conditions first.13,1

"Slow Kill" Treatment

"Slow kill" uses monthly preventives, sometimes with the antibiotic, to kill adult worms gradually over a year or more. AHS says "any method utilizing only MLs as a slow-kill adulticide is not recommended."1 Damage continues while worms remain, strict rest is needed for many months, and it may encourage resistant worms.15,1 AHS calls it "a salvage procedure, not a treatment of choice."15 A 2026 review found high success rates with these protocols in mostly mild cases, and they're used where the adulticide isn't available.16,17 If your dog can't have standard treatment, discuss options and monitoring with your vet.18,6

Cost

A 2026 study found treatment averaged $1,457 per dog, about eight times the cost of a year of prevention.5 PetMD estimates $600 to more than $3,000, depending on size and severity.14 Low-cost community clinics have treated dogs for a few hundred dollars.9 If cost is a concern, ask your vet about payment plans, or contact local shelters or humane societies about low-cost programs. Don't try home remedies: no natural treatment is proven to kill heartworms.19,4

After Treatment

Keep your dog on year-round prevention for life to prevent reinfection.2 If the antigen test is still positive at 9 months, the antibiotic and two injections may be repeated.3 VCA notes that "many owners are surprised at the improvement they see after treatment."20

Frequently Asked Questions

How long does heartworm treatment take?

About 5 months of treatment and strict rest, with a final test at about 1 year.

Can my dog jump on the couch during heartworm treatment?

No. Avoid jumping and all exercise until your vet says otherwise.

Can I treat heartworms at home?

No. Treatment needs vet-given injections and monitoring.

What is the survival rate for heartworm treatment?

Recent studies report about 1% of dogs dying during treatment.

Do dogs poop out heartworms after treatment?

No. Dead worms are broken down in the lungs.

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Sources and further reading

This article was rewritten and fact-checked on October 24, 2026 against current veterinary references and specialist guidelines:

  1. Nelson CT, McCall JW, Moorhead A, Starkey L, Ames M. Canine Guidelines for the Prevention, Diagnosis, and Management of Heartworm (Dirofilaria immitis) Infection in Dogs. American Heartworm Society, revised 2024.
  2. American Heartworm Society. Heartworm Positive Dogs. American Heartworm Society.
  3. American Heartworm Society. Canine Heartworm Guidelines: Highlights. American Heartworm Society, 2024.
  4. US Food and Drug Administration. An Ounce of Prevention is Worth a Pound of Cure: Protect Your Pet from Heartworms Year-Round. FDA Consumer Update, 2023.
  5. Mwacalimba K, Ferguson B, Brennan C, Poulsen Nautrup B, Little J, Stiefelmeyer K, Moldavchuk M, Mosko A, et al. Treatment of heartworm (Dirofilaria immitis) disease in dogs in the USA: general findings and cost of disease. Parasites & Vectors, 2026.
  6. Companion Animal Parasite Council. CAPC Guidelines: Heartworm. CAPC, updated January 2026.
  7. Barnes C, Williams K, Barnette C, Ward E. Heartworm Disease in Dogs: Treatment. VCA Animal Hospitals, updated July 2026.
  8. Maerz I, Rutjes S, Genz S, et al. Adulticide treatment with an arsenic-based adulticide: outcome in 283 heartworm-positive dogs in Germany. Parasites & Vectors, 2026.
  9. Still MB, Tedesco D, Hawkins C, Putnam H. Improving access to arsenic-based adulticide therapy: treating canine heartworm infection in a high-volume, outpatient community clinic setting. Parasites & Vectors, 2024.
  10. McCall JW, DiCosty U, Mansour A, Fricks C, McCall S, Dzimianski MT, et al. Inability of Dirofilaria immitis infective larvae from mosquitoes fed on microfilaremic dogs during short tetracycline-class antibiotic and macrocyclic lactone regimens to develop normally in heartworm-naive dogs. Parasites & Vectors, 2023.
  11. McCall JW, Mansour A, DiCosty U, Fricks C, McCall S, Carson B, et al. Blocking Dirofilaria immitis transmission by treatment of heartworm microfilaremic dogs with a tetracycline-class antibiotic. Parasites & Vectors, 2026.
  12. Xue J, Fuller E, DiGangi B, Donnett U. The American Heartworm Society and Association of Shelter Veterinarians' 2024 Shelter Heartworm Management Practices Survey. Parasites & Vectors, 2026.
  13. Ames MK. Heartworm Disease in Dogs, Cats, and Ferrets. Merck Veterinary Manual, updated August 2026.
  14. Sulik K. Heartworm Treatment Costs for Dogs: What To Expect When Treating Heartworms in a Dog. PetMD, updated April 2025.
  15. Moorhead A. The AHS Protocol vs. "Slow Kill". American Heartworm Society, 2018.
  16. Santiwattanatarm T, Sakcamduang W, Kongkaew C, Anothaisintawee T, Taechikantaphat M. A systematic review and meta-analysis of non-arsenical adulticide protocols using a macrocyclic lactone and a tetracycline-class antibiotic for adult heartworm infection in dogs. Current Research in Parasitology and Vector-Borne Diseases, 2026.
  17. Dantas-Torres F, Ketzis J, Perez Tort G, Mihalca AD, Baneth G, Otranto D, et al. Heartworm adulticide treatment: a tropical perspective. Parasites & Vectors, 2023.
  18. Geary TG. Current issues in heartworm chemotherapy. Parasites & Vectors, 2026.
  19. American Heartworm Society. Are there natural ways to prevent heartworms? American Heartworm Society fact sheet.
  20. Barnes C, Williams K, Weir M, Barnette C, Ward E. Heartworm Disease in Dogs. VCA Animal Hospitals, updated June 2026.

About this article

Last updated : written using the 2024 American Heartworm Society canine guidelines, 2026 Companion Animal Parasite Council recommendations, the FDA, the Merck Veterinary Manual, VCA and 2023 to 2026 treatment studies, plus International Veterinary Information Service (IVIS) proceedings and research published 2022 to 2026.

This page is for general information and is not a substitute for an exam by your veterinarian.