Heartworm Lifecycle Timeline
| Aspect | Prevention | Treatment |
|---|---|---|
| Cost per Year | $100–$250 | $1,000–$3,000 |
| Vet Visits | 1 (annual test) | 3+ (staging+injections) |
| Injections | None | 2–3 deep IM injections |
| Activity Restriction | None | 4–8 weeks strict crate rest |
| Recovery Rate | N/A | 90–95% if caught early |
| Side Effects | Minimal (rare) | Pain, abscess, pulmonary issues |
| Risk to Pet | Near zero | Pulmonary embolism risk |
Year-Round Prevention Protocol
Heartworm Prevention Checklist
| Do | Give monthly preventive year-round (no seasonal gaps) |
| Do | Test annually — even on consistent prevention |
| Do | Test again if you miss more than 1 month of doses |
| Do | Use species-specific product (dog vs cat formulations differ) |
| Do | Keep written log of each dose date |
| Do | Store meds properly (not in extreme heat/cold) |
| Avoid | Assume indoor-only pets don't need prevention |
| Avoid | Skip testing because the dog is 'clearly healthy' |
| Avoid | Use expired preventives to save money |
Heartworm Prevention: What Every Pet Owner Needs to Know
Heartworm disease kills thousands of dogs and cats every year in the United States and is present in all 50 states. It is entirely preventable. Treatment for dogs — once infected — involves months of strict crate rest, injections, and significant expense. There is no approved treatment for cats. Prevention is the only rational choice.
This article is educational. Consult your veterinarian for heartworm testing and to determine the right prevention product for your pet.
| Product | Species | Frequency | Also Covers |
|---|---|---|---|
| Heartgard Plus | Dogs | Monthly oral | Roundworm, hookworm |
| Revolution | Dogs and cats | Monthly topical | Fleas, ear mites, roundworm |
| Interceptor Plus | Dogs | Monthly oral | Roundworm, hookworm, whipworm, tapeworm |
| ProHeart 6 / 12 | Dogs | Injectable (6 or 12 months) | Hookworm |
Why Annual Testing Matters Even on Prevention
Prevention is highly effective but not 100% infallible. A missed dose, a dog that vomits the pill, or a rare breakthrough infection means a dog on year-round prevention could still become infected. Annual heartworm testing (a simple blood test at your annual vet visit) catches any rare breakthroughs early, when treatment is most effective and least risky.
Starting Prevention Without a Test
Dogs over 7 months of age should be tested before starting prevention. Starting prevention in an already-infected dog can cause a serious reaction as microfilariae die rapidly. Puppies under 7 months can start prevention without testing, as it takes that long for heartworms to mature enough to be detectable. Ask your vet before starting any heartworm prevention.
Frequently Asked Questions
How is heartworm transmitted to pets?
Heartworm (Dirofilaria immitis) is transmitted by mosquito bites. A mosquito bites an infected animal, picks up microfilariae (baby heartworms), and deposits them in the next animal it bites. The larvae migrate through tissue and ultimately take up residence in the heart and pulmonary arteries.
Does my indoor pet need heartworm prevention?
Yes. Mosquitoes enter homes regularly. The American Heartworm Society recommends year-round prevention for all dogs and cats, regardless of whether they live primarily indoors or outdoors.
Can cats get heartworm?
Yes, though cats are not the ideal host and typically carry fewer worms. Feline heartworm disease is harder to diagnose, has no approved treatment, and can cause sudden death. Prevention is essential because there is no treatment option for infected cats.