Heartworm treatment is one of the more expensive things that can happen to a dog that otherwise seems healthy. A straightforward case usually costs somewhere around $700 to $2,000, and larger dogs or more advanced disease push it past $3,000.
Owners facing that bill often hear about a cheaper route: skip the injections, keep the dog on monthly preventive with an antibiotic, and let the worms die off slowly. It does cost less up front. But the American Heartworm Society (AHS) calls it a salvage procedure rather than a treatment of choice, and once you see what the money in the standard protocol actually pays for, it is easy to see why.
Where the Money Goes
Itemized US price ranges for a dog going through the standard protocol, as reported by PetMD:
| Step | Typical cost |
|---|---|
| Confirmatory test (a second, different test) | $20–$40 |
| Chest X-rays | $125–$200 |
| Echocardiogram, if your vet needs one | $300–$1,000 |
| Doxycycline course | $30–$150 |
| Steroids | $10–$40 |
| Three melarsomine injections, including hospital time | $500–$1,500 |
| Follow-up test around day 120 | $20–$40 |
| Antigen test around nine months after diagnosis | $35–$75 |
Without an echocardiogram, those lines add up to roughly $740 at the low end and about $2,050 at the high end. That is where the $700–$2,000 figure comes from. Specialist imaging, a dog with advanced heart and lung changes, or hospitalization for complications pushes the total higher, and the rare dogs with so many worms that they must be surgically removed can run $3,000–$6,000.
The original positive test isn’t on this list because you have usually paid for it already. If you are still at the testing stage, our guide to heartworm test cost explains what a positive or negative result can and can’t tell you.
Why a Bigger Dog Costs More
The largest single line on the bill — the melarsomine injections — is dosed by body weight. Across three injections, a 90 lb dog needs several times the drug a 20 lb dog does. The steroids and doxycycline given alongside are weight-dosed too.
So a Labrador and a Beagle diagnosed on the same day at the same clinic can get very different bills, even with the same severity of disease. If you are budgeting, ask your vet for an estimate based on your dog’s actual weight rather than relying on a national average.
Severity matters as well. A dog caught early on an annual test, with no symptoms, usually needs less imaging and monitoring than a dog that came in coughing and struggling with exercise.
What the Standard Protocol Looks Like
The AHS protocol is spread over several months on purpose. Approximate timeline:
| When | What happens |
|---|---|
| Diagnosis (day 0) | Positive confirmed; monthly preventive started; exercise restriction begins |
| First month | Doxycycline course; steroids as your vet directs |
| Around day 60 | First melarsomine injection |
| Around days 90 and 91 | Second and third melarsomine injections |
| Around day 120 | Test for microfilariae |
| About nine months after diagnosis | Antigen test to confirm the adult worms are gone |
Two parts of this surprise most owners.
The killing drug isn’t given first. The month of doxycycline targets Wolbachia, bacteria that live inside heartworms, which weakens the worms and makes their death less inflammatory. The preventive started at diagnosis clears younger larvae, so fewer worms are left to mature while treatment is under way. The two-month wait before the first injection is part of the treatment, not a delay.
The hardest part isn’t the money. Dying worms break up and lodge in the lungs, and exercise raises the risk of a dangerous reaction while that happens. Dogs are kept strictly rested — crate rest and short leash walks only — from diagnosis until the vet clears them after the injections. For a young, energetic dog, those months are often the most difficult part of treatment for the owner.
The “Slow Kill” Route: Why Cheaper Isn’t Cheaper
“Slow kill” means skipping melarsomine and relying on a monthly preventive, usually with doxycycline, to kill the adult worms gradually. It avoids the most expensive line on the bill, which is why it gets suggested.
The American Heartworm Society’s position is blunt. According to AHS:
- slow kill can take up to a year, sometimes much longer, and the timing of worm death is unpredictable
- it is less effective at eliminating adult worms than melarsomine
- while the worms are slowly dying, they keep damaging the lung blood vessels — damage that can be permanent
- the dog needs strict exercise restriction for the whole time, which can mean many months or years rather than a few
AHS describes slow kill as a salvage procedure, not a treatment of choice, meaning something for dogs that can’t have melarsomine for medical or other reasons.
So the saving is real only on paper. You trade a known cost and a defined end date for an open-ended period of restriction, continuing damage, and retesting, with a higher chance that the worms aren’t fully cleared. If cost is the obstacle, the more useful conversation with your vet is about payment plans, or about where melarsomine can be given more cheaply, rather than about skipping it.
Does Pet Insurance Cover It?
Accident-and-illness policies can cover heartworm treatment, but with two important limits:
- Not if the infection was found before your coverage started. At that point it is a pre-existing condition, and no policy will pay for it.
- Policies differ on preventable conditions. Some look at whether the dog was kept on prevention. Read the exclusions before counting on it.
There is also a separate safety net many owners don’t know about. Some preventive manufacturers run guarantees that help pay for treatment if a dog becomes infected while on their product, provided it was given as directed and the dog was tested as required. The Zoetis ProHeart guarantee, for example, covers up to $1,000 plus the cost of melarsomine under its conditions. If your dog was on prevention when it tested positive, ask your vet whether a guarantee applies before you pay for treatment.
Cats: No Treatment to Pay For
There is no approved drug to kill adult heartworms in cats, and melarsomine is not used in cats. Treating a cat means managing the symptoms — often with steroids and supportive care — while the worms die naturally, and the costs vary widely with how ill the cat becomes. For cats, monthly prevention is the only real protection.
The Cheapest Heartworm Treatment Is the One You Never Need
The comparison isn’t close. A year of prevention, including the annual test, generally costs a few hundred dollars at most. Treatment costs several times that, takes months, and is hard on the dog. Our Heartworm Prevention Cost Calculator sets a year of prevention by product type against the cost of treatment for your dog’s size.
If your dog has just tested positive, the practical order of steps is:
- Confirm the result with a second, different test, as most vets will recommend.
- Ask for a written estimate based on your dog’s weight and what the X-rays show.
- Check for a manufacturer guarantee if the dog was on prevention.
- Start exercise restriction now, not when the injections begin.
Frequently Asked Questions
How much does heartworm treatment cost for a dog? Added up item by item, an uncomplicated case typically comes to roughly $700–$2,000: a confirmatory test, chest X-rays, a month of doxycycline, steroids, three melarsomine injections with hospital time, and follow-up tests. Large dogs, advanced disease or extra imaging such as an echocardiogram push the total past $3,000, and the rare cases that need worms surgically removed cost more again.
Why does heartworm treatment cost more for bigger dogs? The drug that kills adult heartworms, melarsomine, is dosed by body weight, and it is the largest single line on the bill. A 90 lb dog needs several times the drug a 20 lb dog does across the three injections, and the steroids and doxycycline given alongside it are weight-dosed too. Disease severity matters as well, because a dog with more advanced heart and lung changes needs more imaging and closer monitoring.
Is slow-kill heartworm treatment cheaper? It looks cheaper because it uses monthly preventive and doxycycline instead of melarsomine injections, but the American Heartworm Society does not recommend it as a treatment of choice. Slow kill can take a year or much longer to work, it is less effective at eliminating adult worms, the worms keep damaging the lungs while they slowly die, and the dog has to stay exercise-restricted the whole time. AHS describes it as a salvage procedure for dogs that cannot have melarsomine.
How long does heartworm treatment take? Under the American Heartworm Society protocol, roughly three months of active treatment and about nine months until the final check. Prevention and a month of doxycycline start at diagnosis, the first melarsomine injection is given around day 60, the second and third around days 90 and 91, and the dog is tested again around day 120 and about nine months after diagnosis. Exercise restriction runs from diagnosis until your vet clears the dog after the injections.
Does pet insurance cover heartworm treatment? Many accident-and-illness policies can cover it, but never if the infection was found before coverage started, because it is then a pre-existing condition. Policies also differ on how they treat preventable conditions and what proof of prevention they expect, so read the exclusions before relying on it. Some preventive manufacturers run their own guarantee that helps pay for treatment if a dog becomes infected while on their product and tested as required.
Can heartworm be treated in cats? There is no approved drug to kill adult heartworms in cats, and the melarsomine used in dogs is not used in cats. Treatment for a cat focuses on managing the symptoms, often with steroids and supportive care, while the worms die naturally over time. That is why monthly prevention is the only real protection for cats.
Related Articles
- Heartworm Test Cost — and Why a Negative Result Is Months Out of Date — what a test can and can’t tell you
- Heartworm Prevention Cost Calculator — a year of prevention against the cost of treatment
- Pet Insurance Cost Estimator — what accident-and-illness cover costs before you need it
- How Much Does a Vet Visit Cost?