Heartworm disease is one diagnosis no dog parent ever wants to hear — and for good reason.
It’s serious, potentially fatal, and far easier to prevent than to treat. Still, many pet parents aren’t quite sure how heartworms work, what the warning signs look like, or what happens if a dog is diagnosed.
This guide breaks down everything you need to know about heartworm disease in dogs — from transmission and symptoms to treatment and prevention.
What Is Heartworm Disease in Dogs?
Heartworm disease is a dangerous parasitic infection in which long, thread-like worms live in a dog’s heart and nearby blood vessels.
These worms typically lodge in the pulmonary arteries — the vessels that carry blood from the heart to the lungs — where they can cause inflammation, restricted blood flow, and serious organ damage. When heartworms die, they can also create blockages that lead to life-threatening complications.
In addition, your dog’s immune response to the infection can further damage the heart and lungs, making the disease especially dangerous if left untreated.
How Do Dogs Get Heartworms?
Dogs can only get heartworms one way: through the bite of an infected mosquito.
When a mosquito bites an infected animal, it picks up immature heartworm larvae. If that mosquito then bites your dog, it transmits the larvae into his bloodstream. From there, the larvae migrate through the body and eventually reach the heart, where they mature into adult worms.
The silver lining? Heartworms are not contagious between dogs, and mosquitoes are the sole source of transmission.
Symptoms of Heartworm Disease in Dogs
One of the scariest aspects of heartworm disease is how silent it can be.
Many dogs show no visible symptoms at all, especially in the early stages. When symptoms do appear, they’re often vague and easy to mistake for other health issues — which is why routine testing is so important.
Possible signs of heartworm disease include:
- Persistent coughing
- Difficulty breathing or shortness of breath
- Swollen abdomen due to fluid buildup
Because much of the damage occurs internally, annual heartworm screenings are essential — even for dogs that seem perfectly healthy.
Heartworm Treatment for Dogs
Treating heartworm disease is a lengthy and demanding process.
Dogs undergoing treatment require multiple medications, including antibiotics, steroids, heartworm preventatives, and injections to kill the adult worms. Hospitalization and strict monitoring are often part of the protocol.
Treatment must be followed exactly as prescribed. Skipping steps or allowing too much activity can significantly increase the risk of complications.
Is Heartworm Treatment Painful for Dogs?
Unfortunately, yes — heartworm treatment can be uncomfortable.
The medication used to kill adult heartworms (melarsomine) is powerful and arsenic-based. It’s administered via deep muscle injections, which can cause soreness, inflammation, and discomfort at the injection site.
This is another reason why prevention is always the preferred option.
Caring for Your Dog After Heartworm Treatment
Recovery is just as important as treatment itself.
After treatment, dogs must remain strictly inactive for several weeks. Exercise or excitement during recovery can cause dead worms to move through the bloodstream, leading to dangerous blockages.
Your role is to help your dog rest, stay calm, and heal — even when he starts acting like he feels better.
How To Prevent Heartworm Disease in Dogs
The best news of all? Heartworm disease is highly preventable.
There are several safe and effective options available, including:
- Monthly oral preventatives
- Injectable preventatives administered by your vet
Some oral medications also protect against fleas and ticks, offering added convenience. All heartworm preventatives work by killing larvae before they can mature and reach your dog’s heart.
Your veterinarian can help you choose the best option based on your dog’s lifestyle and health needs.
The Bottom Line
Heartworm disease is serious, painful, and costly to treat — but incredibly easy to prevent.
Staying consistent with heartworm prevention and scheduling regular vet screenings can spare your dog from a life-threatening illness and months of recovery. A small monthly step can make a life-saving difference 🐾
