What You Should Know About Heartworm

What You Should Know About HeartwormHeartworm is a serious and potentially fatal disease that can affect dogs and cats. It is caused by foot-long worms (heartworms) that live in the heart chambers, lungs, and blood vessels of infected animals. Here’s a detailed overview of heartworm, including how it is contracted, the medical concerns, prevention, and treatment for dogs and cats.

How is Heartworm Contracted?

 Heartworm is primarily transmitted through the bite of an infected mosquito. When a mosquito bites an infected animal, it picks up microfilariae (immature heartworms) from the animal’s bloodstream. These microfilariae mature into infective larvae within the mosquito. Subsequently, when the infected mosquito bites another animal, it transmits the infective larvae into the animal’s bloodstream, where they mature into adult heartworms over several months.

Medical Concerns

For dogs and especially for cats, heartworm disease can be life-threatening. Adult worms can cause damage to the heart, lungs, and arteries, leading to severe lung disease, heart failure, and other organ damage. In cats, even a small number of adult worms can cause severe respiratory and cardiovascular problems. The severity of heartworm disease in cats is not necessarily related to the number of worms present.


Prevention is the best approach to protect pets from heartworm disease. There are several preventive medications available for both dogs and cats. These medications come in various forms, including monthly chewable pills, topical “spot-on” medications, and injectable medications given every 6 or 12 months. Some preventives only protect against heartworms, while others also protect against intestinal parasites, fleas, ticks, and mites. The American Heartworm Society recommends year-round heartworm prevention for pets without missing even one dose.


Treatment for heartworm disease in dogs can be costly and can be difficult, requiring multiple veterinary visits and months of exercise restriction. It is essential to administer treatment as early in the course of the disease as possible. For cats with heartworm disease, the goal is to stabilize the cat and determine a long-term management plan. Unfortunately, there is no definitive treatment protocol available for cats.

In summary, heartworm is a serious and potentially fatal disease for dogs and cats. Preventive medications are highly effective and should be given on time, every time to be effective. If a pet is diagnosed with heartworms, a veterinarian will prescribe a treatment protocol that must be completed before giving the pet any preventive medication.

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