Heartworm prevention costs money every month, and if your dog has never shown signs of illness, the medication can feel like an unnecessary expense. But the risk is real, and understanding how heartworm disease works makes the case for prevention considerably clearer. This is one of those situations where the cost of prevention and the cost of treatment are not in the same category.
Quick Answer: Do Dogs Need Heartworm Prevention?
Yes. The American Heartworm Society recommends year-round heartworm prevention for dogs, with your veterinarian choosing the right product based on your dog’s age, weight, health, lifestyle, and local risk. Heartworm is transmitted through mosquito bites, and heartworm disease has been reported in dogs in all 50 states, including urban areas. There is no safe skip window. Prevention is low-risk and far less expensive than treatment, which is long, physically hard on the dog, and costly.
How Dogs Get Heartworm
Heartworm (Dirofilaria immitis) is a parasitic worm transmitted through mosquito bites. After a mosquito feeds on an infected animal, the larvae must develop inside the mosquito before they can be passed to another dog through a later bite. Those larvae migrate through the dog’s tissues and eventually reach the pulmonary arteries, where they mature into adult worms over roughly six months.
A single infected dog can harbor dozens of adult heartworms. The worms restrict blood flow through the heart and lungs. Over time, untreated infection leads to heart failure, lung disease, and organ damage.
The most important thing to know: early-stage heartworm infection has no visible symptoms. You can’t tell your dog is infected until the disease is well established.
What Happens If You Skip Heartworm Prevention for Dogs
Here’s where the stakes become concrete.
Treating an active heartworm infection in dogs involves:
- Diagnosis typically involves heartworm antigen testing and microfilaria testing, with chest X-rays and other tests used to evaluate disease severity and guide treatment.
- A stabilization period before treatment begins (weeks to months for severe cases)
- A series of melarsomine injections administered into the back muscles
- Strict exercise restriction is usually needed throughout treatment and for 6 to 8 weeks after the final melarsomine injection, because dying worms can increase the risk of serious lung complications.
- Follow-up testing months later to confirm clearance
Treatment runs $1,000 to $1,500 on average, sometimes higher depending on infection severity and geographic cost of care. It’s physically demanding for the dog. The exercise restriction alone is difficult for active or large-breed dogs.
By comparison, monthly heartworm prevention runs $6 to $18 per month depending on the product and your dog’s weight. The math is straightforward.
It’s also worth noting that most monthly preventives cover more than heartworm alone. Many formulations also protect against certain intestinal parasites, such as roundworms and hookworms, and some products may cover whipworms or other parasites depending on the active ingredients. Some products add flea protection, tick protection, or both, depending on the formulation. If you have cats in the household, use only cat-labeled flea and tick products for cats, and ask your veterinarian before using dog-labeled products around cats because some dog products can be toxic to cats.
Heartworm Prevention for Dogs: What Your Options Are
Several effective formulations exist, all requiring a prescription from your vet.
Oral monthly preventives: The most common format. Products like Heartgard, Interceptor, and Sentinel are chewable and given once a month. Highly effective when given consistently on schedule.
Topical monthly preventives: Applied to the skin, typically at the back of the neck. Some owners prefer this approach for dogs resistant to oral medication.
Injectable prevention (ProHeart 6 and ProHeart 12): Given by your vet every 6 or 12 months. A strong option for owners who find monthly consistency difficult to maintain.
The key is consistency. If a dose is late or missed, larvae from a recent mosquito bite may survive and develop. Missing one month isn’t a guarantee of infection, but it removes the protection exactly when your dog may have been exposed. Talk to your vet about which format fits your routine and your dog’s size.
The Urban Dog Misconception
Brooklyn and NYC dog owners sometimes assume their dogs are at lower risk. “We live in a city. Mosquitoes aren’t really a problem here.”
That’s not accurate. Mosquitoes breed in any standing water, including street puddles, flower pots, clogged gutters, and drainage areas. Prospect Park, McCarren Park, Ft. Greene Park, and every green space in the boroughs supports mosquito populations during warmer months. Indoor dogs get bitten through open windows.
Urban dogs do get heartworm. It’s less prevalent here than in the Southeast, where the disease is most common, but the American Heartworm Society recommends year-round prevention in every region of the country, without exception.
While managing your parasite prevention plan, flea risks for urban dogs are worth knowing about too. Dog parks and green spaces in Brooklyn are prime flea environments. And Lyme disease in dogs is a genuine risk for any dog that spends time outdoors in the Northeast, not just in rural areas.
Final Thoughts: Year-Round Heartworm Prevention for Dogs
Dogs really do need heartworm prevention. Every dog, every month, every year. The medication is low-risk, far less expensive than treatment, and effective when given consistently. The disease it prevents is serious, expensive to treat, and entirely avoidable.
If your dog is overdue for a heartworm test or you want help choosing the right prevention plan, contact The Vet Set or book an appointment online. We’re at 577 Henry Street in Carroll Gardens.