Treatment

Heartworm treatment works — but it is a significant process that takes several months and requires strict management at home. The standard protocol recommended by the American Heartworm Society involves multiple steps:

Step 1 — Stabilization and preparation Before treatment begins, your vet will assess your dog's overall health. Dogs with severe disease may need supportive care (steroids, rest) to stabilize before adulticidal treatment starts. A heartworm preventive is started immediately to prevent new infections.

Step 2 — Doxycycline (antibiotic, 28 days) This is an important and often misunderstood step. Heartworms carry a bacteria inside their bodies that is released when being killed. This bacteria can cause severe inflammation in the lungs and raises the risk of dangerous blood clots. A 28-day course of doxycycline kills the bacteria, reduces that risk, and weakens the worms — making the next step more effective.

Step 3 — Melarsomine injections (the adult worm kill) Melarsomine is an FDA-approved injectable drug that kills adult heartworms. It's given in three doses:

• Injection 1: Day 60 — kills a portion of the worms (spreading out the die-off reduces clotting risk)

• Injection 2: Day 90

• Injection 3: Day 91 (24 hours after Injection 2) — this pair delivers the most effective worm kill

Step 4 — Strict rest, the entire time This is the hardest part for most families. From the very first day of treatment until 6–8 weeks after the final injection — roughly 3–4 months total — your dog must be kept as calm and still as possible. No running, jumping, playing, or off-leash time.

Here's why: As the worms die, their bodies can break apart and travel to the lungs as blood clots. A dog that is resting allows the dead worm tissue to dissolve slowly and safely. A dog that is running or playing can dislodge those fragments suddenly, causing a life-threatening pulmonary embolism — even if they seem to feel perfectly fine.

Step 5 — Follow-up testing About 4 months after the last injection, your vet will retest to confirm the treatment worked.