Heartworm disease is one of the most serious and potentially fatal conditions a dog or cat can face, yet it is also one of the most preventable. Spread through the bite of an infected mosquito, heartworms can grow and multiply inside a pet’s heart, lungs, and surrounding blood vessels, causing lasting damage long before any visible symptoms appear. By the time many pets show signs of illness, the disease has already progressed significantly, making early and consistent prevention far more valuable than treatment.
At Montclair Veterinary Associates, we take heartworm prevention seriously as part of our commitment to comprehensive, year-round care for dogs and cats throughout Montclair and the surrounding communities. Led by Dr. Cory Waxman, a University of Pennsylvania School of Veterinary Medicine graduate who has been practicing in Northern New Jersey for more than a decade, our team helps pet owners stay ahead of this preventable disease with routine testing, personalized prevention plans, and straightforward guidance.
Heartworm disease is caused by a parasitic worm called Dirofilaria immitis, which is transmitted exclusively through mosquito bites. When a mosquito feeds on an infected animal, it picks up microscopic larvae called microfilariae. Those larvae develop inside the mosquito and are then deposited onto another animal during a subsequent bite. Once inside a new host, the larvae migrate through the tissues and eventually reach the heart and pulmonary arteries, where they mature into adult worms that can grow to over a foot in length.
Some pet owners assume heartworm is only a concern in warmer, southern states, but that is not accurate. Heartworm disease has been confirmed in all 50 states, and mosquito activity in New Jersey during spring, summer, and fall creates a real window of risk each year. Indoor pets are not exempt either, as mosquitoes regularly enter homes and can bite pets that rarely go outside.
According to the American Veterinary Medical Association, all dogs should be tested annually for heartworm infection, including those that spend most of their time indoors or go outside only occasionally. Annual testing is recommended because heartworm preventives, while highly effective, are not infallible. A missed dose, a late administration, or an unusual exposure event can leave a pet vulnerable without the owner realizing it.
Confirmed in all 50 states. Indoor pets are not exempt — mosquitoes regularly enter homes. Contact our office to schedule annual testing.
Heartworm testing is a straightforward process that can be completed during a routine wellness visit. For dogs, we typically perform an antigen test that detects proteins released by adult female heartworms into the bloodstream. This test is highly accurate and provides results quickly, allowing us to determine whether prevention is working or whether further evaluation is needed.
We generally recommend testing dogs annually, even when they are on a consistent prevention regimen. For dogs with an unknown prevention history or a lapse in medication, we may recommend testing before starting a new preventive and again several months later to account for the window period before adult worms become detectable. Cats are handled somewhat differently, and we evaluate each feline patient individually to determine the most appropriate testing approach.
In the early stages, many pets with heartworm infection show no symptoms at all. As the disease progresses, warning signs may include the following:
😮💨 Persistent Coughing
Often one of the first noticeable signs in dogs, particularly after mild activity.
🐾 Fatigue or Exercise Intolerance
Pets may tire quickly during walks or play sessions that previously posed no difficulty.
🫁 Difficulty Breathing
Labored or rapid breathing may develop as the worm burden increases in the pulmonary arteries.
⚖️ Weight Loss & Reduced Appetite
Systemic effects of the infection can affect overall health and energy levels. Not every pet will display all of these signs, and cats in particular may show subtle or intermittent symptoms. Any of these changes warrants a prompt visit to rule out heartworm or other underlying conditions.
The good news is heartworm disease is highly preventable with consistent use of veterinarian-recommended medications. Prevention options include monthly oral chewables, topical treatments applied to the skin, and injectable options administered by a veterinarian. All of these work by eliminating the larval stages of heartworm before they mature into adults, and they are most effective when given consistently throughout the year.
We do not take a one-size-fits-all approach to prevention. During your pet’s routine health examination, we consider your pet’s age, species, weight, lifestyle, and overall health history before recommending a specific product. We also discuss year-round parasite prevention more broadly, because many heartworm preventives provide protection against intestinal parasites, fleas, and other threats present in our region. If your pet requires prescription medications as part of an ongoing care plan, our prescription pet medications and supplies are available to keep their regimen uninterrupted.
At Montclair Veterinary Associates, we are a locally owned practice rooted in the Montclair community, and we believe preventive care is the foundation of a long, healthy life for your pet. Dr. Waxman and our team bring genuine investment to every appointment, treating each patient as an individual rather than fitting them into a generic protocol. Our approach to heartworm care reflects that same philosophy: we test thoughtfully, recommend purposefully, and stay available to answer your questions along the way.
Heartworm disease is serious, but with regular testing and a consistent prevention plan, it is entirely manageable. If your pet is due for a heartworm test or you have questions about which prevention option is right for them, we encourage you to reach out through our contact form to schedule an appointment with our team.
Most healthy dogs should be tested for heartworm annually, even when they are on a consistent prevention regimen. The American Veterinary Medical Association recommends annual testing for all dogs, including those that spend most of their time indoors. Dogs with a lapse in prevention or an unknown medication history may need additional testing, including a baseline test before starting a new preventive and a follow-up test several months later.
Yes. Heartworm preventives are highly effective, but they are not infallible. A missed dose, a late administration, or an unusual exposure event can leave a pet vulnerable without the owner realizing it. This is one of the main reasons annual testing is recommended even for pets on a consistent prevention schedule, since testing helps catch a breakthrough infection before it causes significant damage.
Yes, indoor pets are absolutely at risk. Mosquitoes regularly enter homes through open doors, windows, and screens, and a single bite from an infected mosquito is all it takes to transmit heartworm larvae. Heartworm disease has been confirmed in all 50 states, and assuming an indoor lifestyle provides full protection is one of the most common misconceptions we address with pet owners.
For dogs, we typically use an antigen test that detects proteins released by adult female heartworms into the bloodstream, which is accurate and provides quick results. Cats are handled somewhat differently since they are a less common host and the disease often presents without typical warning signs. We evaluate each feline patient individually to determine the most appropriate testing approach for their specific situation.
A positive test result is not a reason to panic, but it does call for prompt next steps. We will discuss treatment options based on the severity of the infection, your pet’s overall health, and how far the disease has progressed. Treatment is more involved and carries more risk than prevention, which is exactly why annual testing and consistent prevention are so strongly emphasized. We will walk you through every step of the process and answer your questions along the way.
