Heartworm Prevention for Dogs: The Complete Guide
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Heartworm disease is deadly but almost entirely preventable. Here's how monthly prevention works, what it costs, and how to keep your dog protected.
Heartworm disease is one of the most serious — and most preventable — threats to your dog's health. A single mosquito bite can transmit larvae that mature into foot-long worms living in the heart and lungs. Left unprevented, it can be fatal, and treatment is far more expensive and grueling than prevention. This guide covers everything you need to know about heartworm prevention for dogs.
What heartworm disease actually is
Heartworms (*Dirofilaria immitis*) are spread exclusively by mosquitoes. When an infected mosquito bites your dog, it deposits larvae that migrate to the heart and lungs over about six months, where they grow and reproduce. By the time symptoms appear — coughing, fatigue, weight loss — significant damage may already be done.
Prevention is simple and affordable
A monthly chew like [Heartgard Plus](/products/heartgard-plus-chewables) interrupts the parasite's life cycle before larvae can mature. Most preventives also treat common intestinal worms like roundworm and hookworm, giving you two-in-one protection in a single tasty chew.
Compare that to heartworm *treatment*, which can cost thousands of dollars, requires months of strict rest, and carries real risk. Prevention is by far the smarter investment.
Why year-round dosing matters
Consistency is everything. Because it takes months for larvae to mature, a preventive given today actually clears the infection your dog may have picked up weeks ago. Skipping even one month leaves a gap. Most veterinarians recommend year-round dosing — mosquitoes can survive indoors and during mild spells, and year-round protection removes the risk of a forgotten spring restart.
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Frequently asked
- Does my dog need a heartworm test before starting prevention?
- Yes. Vets test first because giving a preventive to an already-infected dog can trigger a dangerous reaction. Annual testing is recommended thereafter.
- Is year-round heartworm prevention necessary in winter?
- Most veterinarians recommend it. Mosquitoes can survive indoors and during warm spells, and year-round dosing removes the risk of a forgotten spring restart.
- What happens if I miss a heartworm dose?
- Give the missed dose as soon as you remember and resume the schedule. If you've missed more than a couple of months, contact your vet — a retest may be needed before continuing.