Heartworm: The Questions I Finally Asked My Vet

For years I nodded along whenever my vet mentioned heartworm prevention without really understanding what I was preventing. Then I actually asked the questions, and I wish I'd done it sooner.

Heartworm is one of those things owners are told to prevent without ever being told why it matters. I'm not a vet and nothing here replaces one, but I want to lay out the questions I asked and the plain-language answers I came away with, because the topic is far less mysterious once someone explains it like a human.

What actually is heartworm?

Heartworm is exactly what it sounds like: a parasitic worm that can take up residence in and around a dog's heart and lungs. The adult worms are not small. We're talking worms that can grow several inches long living somewhere they absolutely should not be. Left unchecked, they cause real damage, and the early signs an owner might notice include a persistent cough, tiring easily, panting, and general dullness or low energy.

The part that surprised me is that dogs aren't the only species affected. Cats and a range of wild animals can carry it too. Dogs are just the ones most of us are responsible for protecting.

How does a dog even get it?

This was the question that made it click for me: heartworm is spread by mosquitoes. A mosquito bites an infected animal, picks up the immature larvae, and then passes them along when it bites your dog. There's no dog-to-dog contact involved, no shared bowl, nothing you can spot and avoid. If there are mosquitoes where you live, the risk is there.

That also explains the seasonal pattern. In colder months when mosquitoes aren't active, transmission drops off. In warm, humid regions it can be a year-round concern. Knowing it rides on mosquitoes is what finally made prevention make sense to me, and it's why I keep mosquito repellent around the yard in summer as one small extra layer.

Can it be prevented?

Yes, and this is the good news. Prevention is straightforward and routine. Most preventives are given monthly, and the timing my vet explained was to start before mosquito season ramps up and continue past the end of it. In high-risk areas, many owners just dose year-round and don't think about it.

The convenient surprise is that a lot of heartworm prevention products do double duty. The same monthly dose that guards against heartworm often handles intestinal parasites too, so one routine covers several threats. Always get the specific product and dosing from your vet, but ask whether yours is one of these multitaskers.

What forms does prevention come in?

I assumed it was all pills. It isn't. Preventives come as chewable tablets, as topical liquids you apply to the skin between the shoulder blades, and in some cases as an injection your vet administers on a longer schedule. Which one suits your dog depends on the dog, your routine, and your vet's recommendation.

If your dog spits out pills the way mine does, the flavored dog dewormer chews and the topicals are worth asking about. The best preventive is the one you'll actually remember and manage to give every single month, so pick the format that fits your life.

What if a dog already has it?

This was the answer that motivated me to stay on top of prevention. Heartworm can be treated, but treatment is a serious, drawn-out, and expensive process compared to the tiny monthly effort of preventing it. It involves careful medical management and strict rest, and it's hard on the dog. Prevention is dramatically cheaper, easier, and kinder. That contrast alone sold me.

The testing piece

One thing my vet was firm about: you generally test before starting or restarting prevention, because giving certain preventives to a dog that already has an established infection can cause problems. A simple blood test rules that out. So if you've lapsed, don't just quietly restart the monthly dose. Book the test first.

What I do now

My routine is boring, which is the point. Annual vet check, a heartworm test as advised, and a monthly preventive I don't skip. I keep dog flea and tick coverage going alongside it since mosquitoes aren't the only pests out there. None of it is complicated once you understand the why.

If you've been nodding along at the vet without really getting it, ask the questions. Heartworm spreads by mosquito, prevention is a cheap monthly habit, treatment is the expensive nightmare you're trying to avoid, and your vet has the exact product for your dog. That's the whole story, minus the jargon.