Heartworm disease is one of those conditions that’s easy to overlook because you can’t see it happening. There are no obvious early symptoms, no visible signs on the outside. But inside your pet’s body, heartworms can silently damage the heart, lungs, and blood vessels — sometimes before anyone realizes there’s a problem. The good news is that heartworm disease is almost entirely preventable with consistent, year-round care.

How Heartworm Disease Works

Heartworms are parasitic worms transmitted through mosquito bites. When an infected mosquito bites a dog or cat, it deposits microscopic larvae into the skin. Those larvae migrate through the body over several months, eventually settling in the heart and pulmonary arteries where they mature into adult worms that can grow up to a foot long.

In dogs, adult heartworms can multiply and cause progressive damage to the heart and lungs, leading to heart failure and organ dysfunction. In cats, the disease presents differently — even one or two worms can trigger severe respiratory problems, and there is no approved treatment for adult heartworms in cats. For both species, prevention is far safer, simpler, and more affordable than treatment.

How Prevention Works

Heartworm preventives don’t create a barrier against mosquito bites. Instead, they work by eliminating any heartworm larvae that may have entered your pet’s system during the previous month. Most preventives are given monthly as an oral chewable or a topical application. There are also injectable options for dogs that provide protection for six to twelve months.

Consistency is the key. Skipping even one dose can leave a window for larvae to survive and develop into adult worms. That’s why most veterinarians recommend year-round prevention as part of your pet’s wellness care, regardless of season or climate.

Why Annual Testing Still Matters

Even pets on consistent prevention should be tested for heartworm annually. Doses can be missed, pills can be spit out without the owner noticing, and no preventive is guaranteed to be 100% effective in every scenario. A heartworm test is quick and requires only a small blood sample. It’s an important safety check that confirms your pet’s prevention plan is working.

Common Questions About Heartworm

  • Do indoor cats need heartworm prevention? Yes. Mosquitoes get inside through open doors, windows, and screens. A single bite is all it takes to transmit heartworm larvae, so even fully indoor cats are at risk.
  • Can I stop giving prevention in the winter? It’s not recommended. Heartworm prevention needs to be given consistently every month. Gaps in coverage — even during cold weather — can allow larvae to mature into adult worms.
  • Is heartworm treatable in cats? Unfortunately, no. There is no approved treatment for adult heartworms in cats, which makes prevention especially critical for feline companions.

Start Heartworm Prevention in Kirkland, WA

Protecting your pet from heartworm disease is one of the simplest and most impactful things you can do for their long-term health. Finn Hill Animal Hospital can help you choose the right prevention plan and schedule annual testing for your dog or cat. Contact us to book an appointment for pets in Kirkland, Redmond, Bothell, Woodinville, Mill Creek, and surrounding areas.