Heartworm Treatment in Dogs: Rest, Walks, Warning Signs and Care at Home

How dogs get heartworm

• Mosquitoes carry heartworm from one animal to another.
• Heartworm has been diagnosed in all 50 states.
• In the American Heartworm Society's latest survey, based on 2025 testing, Texas had the highest heartworm incidence of any state for the first time, mostly in East Texas.

Sources: 1, 3, 8, 10, 11, 12

Signs to watch for

Many dogs show few or no signs early on. As the disease goes on, signs can include:

• A mild cough that doesn't go away
• Not wanting to exercise, or tiring after moderate activity
• Eating less and losing weight
• A swollen belly, from fluid, as heart failure develops

A dog with many worms can have few or no signs early in the disease. That's why yearly testing matters.

Sources: 1, 3, 4, 7

How vets usually treat it

Your vet chooses the treatment. Here's what to expect with the American Heartworm Society's recommended protocol:

• Confirming the diagnosis with a second, different test before any treatment.
• Stabilizing first, if your dog is showing signs of disease. In severe cases this can take several months.
• About the first month: a heartworm preventive and an antibiotic (doxycycline), and sometimes a steroid to reduce inflammation. Rest starts now: the more signs your dog has, the stricter the rest.
• A one-month wait, then the first injection.
• One month later, two more injections, a day apart. The injections are given into the back muscles, at the veterinary hospital. Melarsomine is the only drug approved by the FDA to kill adult heartworms.
• Strict rest for 6 to 8 weeks after the last injection, then a gradual return to normal activity over about 4 weeks. Some sources give 4 to 6 weeks of rest after the last injection; your vet sets the dates for your dog.
• A retest about 9 months after the last injection to check the worms are gone.

About "slow kill" and home treatment: using a heartworm preventive alone, for a long time, to treat an infection is not recommended by the American Heartworm Society. With those approaches, rest is still required throughout treatment, which can last much longer.

Sources: 1, 2, 3, 4, 6, 8

Caring for your dog at home during treatment

Rest is the main job. Exercise makes the worms damage the heart and lungs faster. After the injections, a fast heart rate from exercise or excitement can push pieces of dead worms into small blood vessels in the lungs. Exercise, excitement and overheating all raise the risk of complications.

Walks

• During the strict phase: on leash when outside, only to urinate and defecate.
• Short, controlled leash walks instead of free yard time, long walks or jogging.
• Many dogs can be safely leash-walked during the recovery period. Ask your vet how long each walk can be.

Confinement

• Keep your dog indoors and in a crate or kennel most of the time.
• If your dog isn't used to a crate, a single quiet room can work instead. Covering a window can cut down on barking and excitement.
• Keep your dog safely confined whenever no one is watching.

Calm things to do

• Chew toys can use up some stored energy.
• Feed part of the daily meal from a puzzle toy or snuffle mat, or freeze some in a chew toy. Use part of the usual meal, not extra food.
• Short training games and new skills, using reward-based training.
• Classical music or audiobooks may help your dog rest. Pheromone sprays or collars may help too.
• If your dog can't settle, tell your vet. Some dogs need medicine to stay calm, alongside these changes at home.

Medicines

• Give each medicine on your vet's schedule, as prescribed, and write it down. The free medication schedule below helps.
• The heartworm preventive is part of treatment, and the American Heartworm Society recommends it year-round, for life, afterward.

Other dogs, daycare and boarding

• Heartworm doesn't spread from dog to dog.
• The sources we use don't cover daycare or boarding by name. They do describe the rest every setting has to keep: crate or quiet room, leash-only bathroom trips, no running or excited play.
• Before daycare or boarding, ask your vet. Give anyone caring for your dog the written rest plan and the warning signs.

Sources: 1, 2, 3, 4, 5, 8, 9

Food

We didn't find published guidance on a special diet for dogs in heartworm treatment. If you use food to keep your dog busy, use part of the usual meal so your dog doesn't gain weight while resting. Ask your vet if your dog needs any change to their food.

Sources: 9

What to expect over time

• Most infected dogs can be treated successfully. Dogs with no signs or mild signs have a high success rate. Dogs with more severe disease can also be treated, with a greater chance of complications.
• The recommended three-injection protocol kills about 98–99% of adult worms. In studies of the American Heartworm Society protocol, about 6.5% of dogs had breathing complications after treatment, and fewer than 1 in 10,000 died.
• Some heart and lung damage can remain even after the infection is cleared. Without treatment, the damage keeps getting worse.
• If the retest is still positive, your vet may recommend a second round of treatment.
• After treatment, year-round prevention and a yearly test help keep your dog from being infected again.

Sources: 2, 3, 4, 7, 14

Find a vet or specialist

• Your own veterinarian is your first call for anything about your dog's heartworm treatment.
• Board-certified specialists in cardiology and small animal internal medicine can help with severe cases. Search by ZIP code on VetSpecialists.com, the American College of Veterinary Internal Medicine's directory.
• In an emergency, go to the nearest emergency animal hospital.

Sources: 13