Dr. Tiffany Delacruz, DVM • Chief Executive Officer, RexVet • 2026-06-22 • 10 min read
Heartworm Prevention for Dogs & Cats: FL, NY & VA Vet Guide
Heartworm prevention is non-negotiable in Florida, New York and Virginia. Which preventives work, and how a $64.99 video visit starts a protocol.
Medically reviewed by Dr. Tiffany Delacruz, DVM
Heartworm disease is one of the most preventable and most devastating parasitic diseases in dogs and cats. This guide is written for pet parents in Florida, New York, and Virginia — the three states where licensed RexVet veterinarians can practice telehealth. It covers why prevention matters in each state, which preventives work for which pets, and how telehealth fits.
What heartworm actually is
Heartworm (Dirofilaria immitis) is a parasitic worm transmitted by mosquitoes. When an infected mosquito bites your dog or cat, it injects larvae that migrate through the bloodstream and mature into adult worms (6-12 inches long) that live in the heart and pulmonary arteries. Adult worms damage the heart, lungs, and blood vessels — eventually causing heart failure.
- Dogs: can carry hundreds of adult worms. Treatment is possible but harsh and expensive.
- Cats: usually carry 1-3 worms. Even one worm can kill a cat. No effective treatment exists.
- Both species: prevention is essentially the only safe approach.
Why prevention matters in FL, NY, and VA
All three states have significant mosquito populations — but the risk pattern differs:
- Florida — Year-round mosquito activity, highest heartworm prevalence in the US for both dogs and cats. The 'gulf coast' strain may be more resistant to some preventives. Florida cats especially are at risk.
- New York — Mosquito season runs roughly May-October. NYC and upstate both have heartworm-positive cases. Climate change is extending the season; year-round prevention is now standard.
- Virginia — Mosquito season runs roughly April-October. NoVA, Richmond, and Hampton Roads all see heartworm cases. The state's high tick load also means many pets are already on combination preventives (heartworm + tick).
Preventives that work — dogs
All of these require a current negative heartworm test (annual blood draw, in-person):
- Heartgard Plus (ivermectin) — monthly chewable, classic, very affordable
- Interceptor Plus (milbemycin + praziquantel) — also covers intestinal parasites
- Sentinel (milbemycin + lufenuron) — also breaks the flea life cycle
- Trifexis (spinosad + milbemycin) — also kills fleas
- Simparica Trio (sarolaner + moxidectin + pyrantel) — also covers ticks and fleas (single product, popular)
- ProHeart 6 / ProHeart 12 (moxidectin injection) — 6 or 12 months of prevention from a single injection (requires vet visit)
Preventives that work — cats
Cats need feline-specific products (do NOT give cats dog preventives — Heartgard for cats is different formulation):
- Revolution Plus — monthly topical, covers heartworm + fleas + ticks + intestinal parasites
- Bravecto Plus — 2-month topical, comprehensive coverage including heartworm
- Advantage Multi for Cats (imidacloprid + moxidectin) — monthly topical
- Centragard (eprinomectin + praziquantel) — monthly topical
Why annual heartworm testing matters
Heartworm preventives kill larvae, not adult worms. If your pet has already been infected with adult worms (from a missed dose, late start, or unknown previous exposure) and you start a preventive, you can trigger a fatal anaphylactic reaction. Annual testing catches infections early when treatment is still possible. The 4Dx SNAP test (in-clinic, requires blood draw) screens heartworm + 3 tick-borne diseases — particularly important in Virginia.
Florida-specific: prevention is mandatory in practice
Florida sees the highest heartworm rates in the US — for both dogs and cats. Year-round mosquito activity, climate, and a large transient pet population mean if your Florida pet isn't on heartworm prevention, you're rolling dice with their life. RexVet FL-licensed veterinarians can prescribe heartworm preventive in a $64.99 video visit where state rules allow, with same-day RexVetRx delivery in most major FL ZIPs when the veterinarian prescribes. In Florida, a veterinarian who has seen your pet only by video may prescribe only FDA-approved animal drugs used as labeled, for up to 14 days (1 month for flea-and-tick-only products), and cannot renew without an in-person exam. Annual 4Dx test in-person is required for ongoing prescription.
New York-specific: indoor cats still need it
NYC apartment cats are NOT safe from heartworm — mosquitoes get into apartments through unscreened windows, elevators, and on shoes. Many NYC pet parents skip feline heartworm prevention thinking 'indoor only = safe' but the reality is single-mosquito exposure can be fatal. Year-round prevention costs ~$15/month — minor expense, life-saving outcome. RexVet NY-licensed veterinarians can prescribe Revolution Plus or Bravecto Plus by $64.99 video visit where state rules allow.
Virginia-specific: combine with tick prevention
Virginia has the heaviest tick load in the eastern US in addition to mosquito-borne heartworm risk. Most VA vets recommend a combination product like Simparica Trio (dogs) or Revolution Plus (cats) that covers both. The 4Dx test screens heartworm + Lyme + anaplasmosis + ehrlichiosis in one blood draw. RexVet VA-licensed veterinarians can prescribe combo preventives where state rules allow and coordinate annual 4Dx testing.
How telehealth fits in
$64.99 RexVet video visits in FL/NY/VA can: prescribe heartworm preventive where state rules allow (with a current negative test on file), review refill requests where state rules allow, coach on the right product for your pet's lifestyle, and triage post-bite or post-exposure concerns. Annual in-person heartworm test required — same-day RexVetRx delivery in most ZIP codes once prescription is approved.
Emergency signals
When to contact a veterinarian
- Coughing in a dog that hasn't been tested — could be advanced heartworm
- Sudden collapse in a cat (with or without breathing changes) — feline heartworm is a critical differential
- Missed multiple doses of heartworm preventive — schedule a test before restarting
- Your pet vomited the heartworm chew — wait an hour, then re-dose
- Adopted a pet of unknown heartworm status — get tested before starting prevention
- Travel to high-prevalence area like the Gulf Coast — make sure prevention is current
Frequently asked questions
Do indoor cats really need heartworm prevention in FL, NY, or VA?
Yes — especially in Florida, but also in NY and VA. Mosquitoes get inside through windows, elevators, on shoes, and via apartment vents. Feline heartworm has no effective treatment and a single worm can be fatal. Year-round prevention via Revolution Plus or Bravecto Plus costs ~$15/month — RexVet FL/NY/VA-licensed vets can prescribe it by $64.99 video visit where state rules allow.
How much does heartworm treatment cost vs. prevention?
Treatment for a heartworm-positive dog runs $1,500-$3,000 in most areas (more in NYC), involves multiple injections with bedrest for months, and carries real risk. Prevention costs $5-$25 per month per pet. The math is straightforward — prevention is dramatically cheaper, safer, and easier.
Can a RexVet online vet prescribe heartworm prevention in Florida, New York, or Virginia?
If the veterinarian decides it is appropriate after a video visit, they can prescribe it where state rules allow. A current negative heartworm test on file (annual blood draw, in-person) is required.
Is year-round heartworm prevention really necessary?
Yes, per the American Heartworm Society and most veterinary specialists. Climate change has extended mosquito season everywhere, and missed doses are common when owners try to seasonally restart. Year-round is the modern standard in all three states.
What's the difference between heartworm and intestinal worms?
Heartworm (Dirofilaria immitis) lives in the heart and lungs and is transmitted by mosquitoes. Intestinal worms (roundworms, hookworms, whipworms, tapeworms) live in the gut and are transmitted via fecal-oral route. Most modern heartworm preventives also cover intestinal worms — check the label.
Florida heartworm — is there really a 'resistant strain'?
The 'gulf coast' or 'MP3' strain shows reduced response to some macrocyclic lactones (ivermectin, milbemycin) in lab settings, but in clinical practice, monthly prevention still works for the vast majority of cases. The bigger issue is missed doses. Stay on schedule, test annually.
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About the author
Dr. Tiffany Delacruz, DVM
Chief Executive Officer, RexVet
Licensed veterinarian and CEO of RexVet (Rex Vets Inc.). Practicing across Florida, New York, and Virginia via licensed telehealth. Reviews every clinical article on RexVet before publication.