Adopting a Heartworm-Positive Dog: Treatment and Costs

Last updated: May 6, 2026

What It Means to Adopt a Heartworm-Positive Dog

Heartworm disease sounds frightening, and the diagnosis often causes potential adopters to hesitate. But adopting a heartworm-positive dog is far less daunting than most people assume. With proper treatment, the vast majority of heartworm-positive dogs recover fully and go on to live normal, healthy lives.

Heartworm disease is caused by parasitic worms (Dirofilaria immitis) that are transmitted through mosquito bites. The worms travel through the bloodstream and eventually lodge in the heart and pulmonary arteries, where they can grow up to a foot long. Left untreated, heartworm disease is fatal. But when caught and treated, the prognosis is excellent.

Dogs in shelters and rescues are frequently diagnosed with heartworm disease, especially in the southern United States where mosquito exposure is year-round. Many of these dogs are passed over by adopters who don’t understand the condition. This guide breaks down everything you need to know — from treatment protocols to costs to what daily life looks like during recovery.

How Heartworm Disease Is Diagnosed and Staged

Before treatment begins, your veterinarian will confirm the diagnosis and determine the severity of the infection. This typically involves:

• Antigen test: A blood test that detects proteins produced by adult female heartworms. This is the standard screening test used by shelters and rescues.
• Microfilaria test: A blood smear that checks for baby heartworms (microfilariae) circulating in the bloodstream.
• Chest X-rays: Show the size and shape of the heart and lungs, revealing how much damage the worms have caused.
• Bloodwork: A complete blood panel assesses organ function and overall health before treatment.

Heartworm disease is classified into four stages:

1. Class 1 (mild): No symptoms or a mild cough. X-rays appear normal or show minimal changes.
2. Class 2 (moderate): Occasional cough, mild exercise intolerance. X-rays show some heart and lung changes.
3. Class 3 (severe): Persistent cough, significant exercise intolerance, difficulty breathing. X-rays show significant heart enlargement and lung changes.
4. Class 4 (caval syndrome): Life-threatening. Worms block blood flow to the heart. Requires emergency surgical removal of worms.

Most dogs available for adoption are in Class 1 or 2, which have the best treatment outcomes. Ask the rescue for the dog’s heartworm classification and any diagnostic results they have.

The Treatment Protocol: What Actually Happens

Heartworm treatment follows a well-established protocol recommended by the American Heartworm Society. Understanding the steps removes much of the anxiety around the process.

Step 1: Pre-treatment stabilization (1-2 months). Your vet will start the dog on a monthly heartworm preventive (like ivermectin) and typically a course of the antibiotic doxycycline. The preventive kills any new larvae, and doxycycline targets a bacterium (Wolbachia) that lives inside heartworms, weakening them before the main treatment.

Step 2: Adulticide injections (melarsomine). This is the core of treatment. The drug melarsomine (brand name Immiticide or Diroban) is injected deep into the muscles along the spine to kill adult heartworms. The standard protocol involves three injections:

• First injection on Day 1
• Second injection 30 days later
• Third injection 24 hours after the second

The injections can cause soreness at the injection site, and your dog may be uncomfortable for a day or two after each one. Your vet will prescribe pain management as needed.

Step 3: Strict rest during treatment (2-3 months). This is the hardest part — not for the dog, but for you. As the adult worms die, they break apart and are absorbed by the body. During this process, fragments can cause blockages in the pulmonary arteries. Exercise increases heart rate and blood flow, which raises the risk of these complications.

Strict rest means: leash walks only for bathroom breaks, no running, no playing, no roughhousing, no stairs if avoidable, and no off-leash time. Crate rest or confinement to a small room is typically recommended.

Managing the Rest Period

The enforced rest period is challenging, especially with an energetic dog. But it’s absolutely critical for safe recovery. Here’s how to keep your dog calm and mentally engaged during this time:

• Frozen Kongs and puzzle feeders: Stuff a Kong with peanut butter (xylitol-free) and freeze it. Puzzle feeders slow down mealtimes and provide mental stimulation without physical exertion.
• Training sessions: Short, calm training sessions (sit, stay, gentle tricks) engage the brain without raising the heart rate. Keep sessions under 10 minutes.
• Sniff mats and nose work: Hide treats in a snuffle mat or around a confined area. Sniffing is mentally tiring for dogs and doesn’t require physical activity.
• Chews and bones: Long-lasting chews like bully sticks or dental chews keep dogs occupied. Supervise all chewing to prevent choking.
• Calm companionship: Sometimes just being near you is enough. Sitting on the couch together, gentle petting, and quiet time all help your dog feel secure during a confusing period.

If your dog is particularly anxious or energetic during the rest period, talk to your vet about mild sedatives or anti-anxiety medication. It’s a short-term solution for a critical phase of recovery.

Costs of Heartworm Treatment

Understanding the financial commitment is essential when adopting a heartworm-positive dog. Here’s a realistic cost breakdown:

• Diagnostic workup (bloodwork, X-rays, antigen test): $200 to $500
• Pre-treatment medications (doxycycline, monthly preventive): $50 to $150
• Melarsomine injections (three-injection protocol): $500 to $1,500, depending on the dog’s size and your geographic area
• Post-treatment follow-up (recheck bloodwork, antigen test at 6 months): $100 to $300
• Medications during treatment (steroids, pain management, preventives): $50 to $200

Total estimated cost: $900 to $2,650.

Many rescues cover some or all of the treatment costs before adoption, especially the pre-treatment phase and sometimes the melarsomine injections. Ask the rescue what has already been completed and what costs you’ll be responsible for. Some rescues partner with veterinary clinics that offer discounted treatment for rescue dogs.

Pet insurance generally does not cover heartworm treatment if the dog was diagnosed before the policy started, since it’s considered a pre-existing condition. However, insurance will typically cover future heartworm prevention once the dog tests negative.

Life After Treatment: Long-Term Outlook

The good news is that most dogs who complete heartworm treatment recover fully. About six months after the final injection, your vet will retest for heartworm antigen. A negative test means the treatment was successful and the adult worms have been eliminated.

After treatment, your dog will need:

• Monthly heartworm prevention for life: This prevents reinfection. Several options are available, including monthly chewables, topical treatments, and an injectable preventive (ProHeart) that lasts 6 to 12 months.
• Annual heartworm testing: Even on prevention, annual testing catches any breakthrough infections early.
• Gradual return to normal activity: Your vet will advise when it’s safe to resume normal exercise. Most dogs can return to full activity within a few weeks of the rest period ending.

Dogs that were treated at Class 1 or 2 typically suffer no lasting heart or lung damage. Dogs treated at Class 3 may have some residual effects, but many still go on to lead active, happy lives. Your veterinarian will monitor your dog’s cardiovascular health as part of routine wellness care.

If you’re ready to give a heartworm-positive dog a chance, browse adoptable dogs at Walk Me Home Rescue. Many of these dogs are already partway through treatment and just need a patient family to see them through recovery. You might also find our guide to adopting dogs with special needs helpful as you explore your options.

Why Heartworm-Positive Dogs Are Worth Adopting

Heartworm-positive dogs are among the hardest to place in rescue. The diagnosis scares people away, and these dogs often languish in shelters or foster homes while healthy dogs get adopted around them. But the reality is that heartworm disease is a treatable condition — not a death sentence.

By adopting a heartworm-positive dog, you’re saving a life that might otherwise be overlooked. The treatment period is temporary, but the bond you build while nursing your dog back to health lasts forever. Many adopters of heartworm-positive dogs say the experience deepened their connection with their pet in ways they never expected.

These dogs didn’t choose to get heartworm disease. A mosquito bite and a lack of preventive care put them in this situation. Your willingness to see past the diagnosis and invest in their recovery is the kind of compassion that defines the rescue community. Visit Walk Me Home Rescue to see who’s waiting for you, and review our adoption application tips to strengthen your application.

Frequently Asked Questions

Can heartworm disease spread to my other dogs?

No. Heartworm is not contagious between dogs. It can only be transmitted through the bite of an infected mosquito. However, if one dog in your area has heartworm, it means infected mosquitoes are present — so make sure all your dogs are on monthly heartworm prevention.

Is heartworm treatment painful for dogs?

The melarsomine injections can cause localized soreness and discomfort at the injection site for one to three days. Your vet will prescribe pain medication to manage this. Most dogs bounce back quickly after each injection. The rest period is more frustrating than painful for most dogs.

What happens if I can’t enforce strict rest?

The rest period is critical for safe recovery. Exercising during treatment increases the risk of dead worm fragments causing a pulmonary embolism, which can be fatal. If your dog is struggling to stay calm, talk to your vet about crate rest strategies, mild sedation, or anti-anxiety medication. The rest period is temporary but non-negotiable.

Can cats get heartworm disease?

Yes, but it presents differently in cats and is harder to diagnose and treat. There is currently no approved adulticide treatment for cats, so prevention is especially important for felines. Talk to your vet about heartworm prevention for all pets in your household.

How long does the entire treatment process take?

From start to finish, heartworm treatment typically takes four to six months. This includes the pre-treatment stabilization period, the three melarsomine injections over about 60 days, and the post-injection rest period. Final testing to confirm the worms are gone happens about six months after the last injection.