If you live in Boca Raton or anywhere else in South Florida, your dog needs heartworm prevention every month, all twelve months of the year, for the entirety of its life — and your indoor cat probably needs it too. South Florida sits inside the highest-incidence heartworm zone in the United States, and our mosquitoes do not take a winter off. The most reliable approach for dogs is a monthly chewable preventive (such as ivermectin, a milbemycin- or moxidectin-based product) paired with an annual heartworm antigen test; for indoor/outdoor cats, a topical monthly product is the standard. Prevention runs roughly $8 to $30 per month at our clinic depending on the pet’s weight and whether the product is heartworm alone or an all-in-one. Treating an established heartworm infection in a dog typically runs $1,000 to $1,500 and carries real risk. The math is not subtle, and neither is the climate. At Regency Veterinary Clinic on Yamato Road, we treat year-round prevention as the standard of care.
This guide explains why South Florida is different, which preventive products we use and why, what the testing protocol actually involves, and what it costs to prevent versus treat heartworm disease in 2026.
Why South Florida is the worst region in the country for heartworm
Heartworm disease is transmitted by mosquitoes carrying Dirofilaria immitis larvae. The disease is endemic across the entire United States, but the American Heartworm Society’s most recent incidence survey ranks the Gulf and South Atlantic states — with Florida, Louisiana, Mississippi, and Texas at the top — as the highest-positive region in the country. Within Florida, South Florida is the most consistently warm, the most consistently humid, and home to mosquito species that bite year-round. In Palm Beach and Broward counties we do not get a real freeze, which means mosquito populations never crash to zero the way they do further north.
Three local realities matter most:
- No off-season. A dog in Massachusetts can plausibly be on prevention nine months of the year. A dog in 33434 cannot — we see positive heartworm tests in January.
- A large parasite reservoir. South Florida’s untreated stray and community dog population keeps infection rates high. Every unprevented dog is a source for the mosquitoes biting your dog.
- Pet movement. Boca families travel, board, foster, and adopt frequently, and we routinely see pets arriving from rural Florida shelters, out-of-state rescues, and the Caribbean — many already heartworm-positive.
The American Heartworm Society publishes a regularly updated incidence map and clinical guidelines that confirm what we see in our exam rooms: South Florida is not an average risk environment, and it does not respond to average risk management.
How heartworm disease actually works in dogs and cats
A mosquito picks up immature heartworm larvae from an infected animal, and roughly two weeks later — when it bites your dog or cat — deposits infective larvae onto the skin. Those larvae migrate through tissue, mature over about six months, and end up as adult worms in the pulmonary arteries and right side of the heart. Adult worms reach 10 to 12 inches and live five to seven years if untreated.
In dogs the disease is slow and progressive: exercise intolerance, a soft chronic cough, weight loss, and eventually right-sided heart failure. By the time symptoms are obvious, significant cardiopulmonary damage has already occurred.
Cats are an atypical host, so worm burdens are usually small — often just one to three worms — but even a single worm can cause heartworm-associated respiratory disease (HARD), which is frequently misdiagnosed as asthma. There is no approved treatment for adult heartworm infection in cats, which is exactly why feline prevention matters for cats who go outdoors.
Prevention products — what we use at Regency and why
There is no single “best” preventive — there are several excellent options, and the right choice depends on the pet’s species, weight, lifestyle, and whether you also want flea, tick, or intestinal-parasite coverage in the same product. We do not stock every brand on the market, because we choose products with the strongest efficacy data and the simplest year-round compliance for the families we serve.
The table below compares the categories of products we either dispense or have available on our online pharmacy.
| Product Category | Form | Pets | What It Also Covers | Typical Monthly Cost (Regency, 2026) |
|---|---|---|---|---|
| Milbemycin oxime chewable (e.g., Interceptor Plus) | Monthly chew | Dogs | Hookworm, roundworm, whipworm, tapeworm | $14 – $22 |
| Moxidectin + afoxolaner chewable (e.g., Nexgard Plus) | Monthly chew | Dogs | Fleas, ticks, hookworm, roundworm | $25 – $33 |
| Ivermectin + pyrantel chewable (e.g., Heartgard Plus) | Monthly chew | Dogs | Hookworm, roundworm | $9 – $13 |
| Moxidectin extended-release injection (ProHeart 12) | One-year injection in clinic | Dogs | Partial hookworm & roundworm | $130 – $250 annually |
| Esafoxolaner, eprinomectin + praziquantel topical (e.g., Nexgard Combo) | Monthly topical | Cats | Fleas, ticks, ear mites, hookworm, roundworm, tapeworm | $22 – $25 |
A few practical notes on choosing between them:
- For most adult dogs in west Boca, a monthly chewable combination product is the easiest path to year-round compliance, because one chew handles heartworm, fleas, and intestinal worms.
- ProHeart 12 is excellent for households where remembering a monthly chew is unreliable — frequent travelers, multi-pet families, or owners caring for a parent’s dog. It is given in the exam room and lasts a full year.
- For Collies, Australian Shepherds, and related herding breeds, we discuss MDR1 genetic status before recommending an ivermectin-based product.
- Coverage gaps matter more than brand loyalty. A skipped month in South Florida is meaningfully different from a skipped month in Vermont.
For a broader sense of how we make recommendations like these, see our local guide to choosing a veterinarian in Boca Raton.
Testing — what the annual heartworm test actually checks
Every dog on prevention should be tested annually, even if you have never missed a dose. No preventive is 100% effective, missed or vomited doses happen more often than owners realize, and a positive test on a dog erroneously given a preventive can cause a dangerous reaction.
The standard annual test is a heartworm antigen test, which detects proteins released by adult female worms — a few drops of blood, results in about ten minutes in-clinic. For positive results, we follow up with a microfilaria test and chest radiographs to stage the disease before treatment.
For new puppies, the first heartworm test is run at the six- to seven-month visit, since it takes about six months from infection for adult worms to produce detectable antigen. Rescue dogs of any age should be tested at intake regardless of paperwork. For cats, antigen-and-antibody combination testing is used, since worm burdens are too low for antigen alone to be reliable.
Cost of prevention versus cost of treatment
This is the comparison that matters most, and it is the one most owners have never seen laid out clearly.
| Scenario | Typical Annual Cost (2026) |
|---|---|
| Year-round prevention, 50-lb adult dog (chewable + annual test) | $200 – $350 |
| Year-round prevention, indoor/outdoor cat (monthly topical) | $340 – $360 |
| Year-round prevention via ProHeart 12 + annual test | $200 – $340 |
| Treating an established canine heartworm infection | $1,000 – $1,500 |
Beyond the financial difference, heartworm treatment is medically aggressive: a series of melarsomine injections into the lumbar muscles, eight to twelve weeks of strict cage rest, and a real (if small) risk of pulmonary thromboembolism as the worms die. It works, but no veterinarian would choose it over prevention. For new clients setting up year-one preventive care, the first vet visit guide walks through how heartworm testing fits into a typical appointment.
Frequently asked questions
Do indoor cats really need heartworm prevention in South Florida?
Yes. Roughly a quarter of cats diagnosed with heartworm disease are reported by their owners as strictly indoor. Mosquitoes come in through doors, screened lanais, and garages, and a single infected mosquito is enough. Combined with the fact that there is no approved adult-worm treatment in cats, prevention is the entire strategy.
What happens if I miss a month of prevention?
For dogs on a monthly chewable, give the missed dose as soon as you remember and continue monthly from there. If the gap was longer than about two months, call us and we will plan a heartworm test six months out, because adult worms take roughly six months to become detectable. Do not double-dose to “catch up.”
Can I buy heartworm preventives online instead of at the clinic?
Yes, and many of our clients do. We are happy to write a prescription. Two cautions: buy only from legitimate U.S. pharmacies, because counterfeit and improperly stored preventives circulate online, and confirm that the product is FDA-approved for use in dogs (not the agricultural large-animal formulation). Many manufacturers also honor their efficacy guarantee only when the product is purchased through a veterinarian.
Are natural or herbal heartworm preventives safe to use?
No. There is no published evidence that any herbal, garlic-based, or essential-oil product prevents heartworm infection, and we routinely diagnose heartworm-positive dogs whose owners used these products in good faith. The FDA does not approve any natural heartworm preventive, and neither the AVMA nor the American Heartworm Society recognizes one.
My dog tested heartworm-positive — can you treat him at Regency?
Yes. We follow the American Heartworm Society protocol: pre-treatment radiographs and bloodwork, a month of doxycycline, and a staged melarsomine injection series with strict exercise restriction. We discuss prognosis, cost, and the activity-restriction reality before starting. Most uncomplicated cases do well.
How early can I start a puppy on heartworm prevention?
Most products are labeled starting at six to eight weeks of age. We begin prevention at the first puppy visit and continue without interruption. No initial heartworm test is needed before the six-month mark because adult worms have not yet matured.
Does heartworm prevention also handle fleas and intestinal worms?
It depends on the product. Several combination chewables (Simparica Trio, Interceptor Plus, NexGard Plus) cover heartworm plus various combinations of fleas, ticks, and intestinal parasites in one monthly dose. We pick a combination based on lifestyle — dog-park regulars and beach dogs benefit from tick coverage; indoor-leaning small dogs may not.
Start or update your pet’s heartworm plan at Regency
If you are new to the area, recently adopted, or simply not sure what your pet is currently on, we are glad to review it with you — bring the box or a photo of the label, and we will tell you straight whether it is the right fit for a South Florida dog or cat.
Call (561) 999-5551 or book online. We are at 3013 Yamato Rd, Suite B6, Boca Raton, FL 33434, serving west Boca, east Boca, Delray Beach, and Parkland families since 2001. You can learn more about our team or browse our full list of services.
Written by Dr. Morgan Tannenbaum, DVM · Regency Veterinary Clinic · Boca Raton, FL
This post is general information and is not a substitute for an in-person veterinary exam. Specific medical recommendations, including which preventive product is appropriate for your pet, require an evaluation by a licensed veterinarian.