If you’d like an overview of the most common parasites that affect dogs — and how they’re treated and prevented — visit our Dog Parasites Guide.
If your dog has been diagnosed with heartworm disease — or if you’re worried about possible exposure — take a deep breath.
Heartworm disease is a serious condition, but it is well understood, manageable, and often treatable, especially when caught early. Many dogs go on to live happy, healthy lives after proper care and treatment.
Your veterinarian is your most important guide through this process. With the right testing, treatment plan, and follow-up care, heartworm disease can be addressed safely and thoughtfully, with your dog’s comfort and long-term health as the top priority.
Learning how heartworms affect dogs, how the disease is treated, and how it can be prevented moving forward can help you feel more confident and prepared as a dog owner — and ensure your dog receives the best possible care.
Heartworm disease is a serious and potentially life-threatening condition that affects dogs worldwide. It is caused by parasitic worms that live in the heart, lungs, and associated blood vessels, leading to severe organ damage if left untreated.
Understanding how heartworms are transmitted, how to recognize early symptoms, and how to prevent infection is essential for protecting your dog’s long-term health.
What Is Heartworm Disease?
Heartworm disease is caused by a parasitic worm (Dirofilaria immitis) that is spread through mosquito bites. Once inside a dog’s body, heartworm larvae mature into adult worms that can grow up to a foot long and live for several years.
As the worms multiply, they interfere with normal heart and lung function, causing progressive and damage. It is important to treat your dog as soon as heartworm is diagnosed.
How Dogs Get Heartworm Disease
Dogs become infected with heartworms through the bite of an infected mosquito. When a mosquito feeds on a dog that already has heartworms, it can pick up microscopic heartworm larvae. Those larvae then develop inside the mosquito and may be passed to another dog during a later bite.
It’s important to know that heartworm disease is not spread directly from dog to dog. Dogs cannot transmit heartworms through casual contact, sharing bowls, playing together, or living in the same household. Heartworms require mosquitoes as part of their life cycle.
Can Humans Get Heartworms?
This is a very common and understandable concern.
Humans do not get heartworm disease from dogs, and heartworms are not contagious to people.
In very rare cases, heartworm larvae may be transmitted to humans through a mosquito bite, but the parasites cannot fully mature or reproduce in the human body. These rare cases typically do not cause the same disease process seen in dogs, and heartworms cannot be passed from humans to others.
Heartworm disease remains primarily a canine health concern, which is why regular prevention and veterinary care for dogs is so important.
Because mosquitoes are widespread and active in many climates — even in cooler regions or indoors — heartworm prevention is recommended year-round for dogs. Preventive medications help stop infection before heartworms can develop, keeping dogs protected and giving owners peace of mind.
Heartworm disease:
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Can affect dogs of any age or breed
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Occurs in all regions, including cooler climates
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Is not spread directly from dog to dog
Because mosquitoes are widespread, heartworm prevention is important year-round. Contact your veterinarian for the proper medication for your dog.
Common Symptoms of Heartworm Disease in Dogs
Symptoms may develop slowly and are often mild in the early stages, making heartworm disease difficult to detect without testing.
Common signs include:
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Persistent cough
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Fatigue after mild activity
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Decreased appetite
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Weight loss
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Difficulty breathing
In advanced cases, dogs may experience heart failure, fluid buildup, or collapse.
Diagnosing Heartworm Disease
Heartworm disease is diagnosed through veterinary testing, most commonly with a simple blood test that detects heartworm proteins or antibodies. These tests are routine, widely used, and an important part of preventive care — even for dogs that appear healthy.
If a test comes back positive, your veterinarian may recommend additional diagnostic tools to better understand how the heartworms are affecting your dog’s body. This allows them to create a treatment plan that is tailored specifically to your dog’s needs and overall health.
Additional testing may include:
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Chest X-rays, which help assess the heart and lungs and look for signs of inflammation or changes caused by heartworms
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Ultrasound, which allows the veterinarian to view the heart and surrounding blood vessels in more detail
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Additional blood work, used to evaluate organ function and ensure your dog is strong enough for treatment
While the word “testing” can feel overwhelming, these steps are taken with care and purpose. Each test provides valuable information that helps your veterinarian choose the safest and most effective treatment path for your dog.
Many dogs are diagnosed early through routine screening, before serious symptoms develop. Early detection gives dogs the best chance for a smooth recovery and a healthy future — and gives owners reassurance that their dog is receiving the right care at the right time.
Routine heartworm testing is recommended, typically once a year, even for dogs receiving preventive medication.
Treatment for Heartworm Disease in Dogs
Treatment for heartworm disease is carefully planned and guided by your veterinarian. While heartworm disease is serious, many dogs respond well to treatment, especially when the condition is diagnosed early and managed thoughtfully.
The exact treatment plan depends on several factors, including how long the dog has been infected, the number of heartworms present, and the dog’s overall health. Your veterinarian will take all of these factors into account when deciding on the safest and most effective approach.
Treatment may involve:
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Medications to eliminate adult heartworms, administered under veterinary supervision
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Antibiotics, which help reduce inflammation and complications associated with the parasites
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Medications to support your dog’s comfort and recovery during treatment
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Strict activity restriction, which is a crucial part of the healing process
Limiting physical activity helps prevent strain on the heart and lungs while the body clears the parasites. Although this period of rest can feel challenging for both dogs and owners, it is temporary and plays a vital role in a successful outcome.
Throughout treatment, your veterinarian will monitor your dog closely. Follow-up visits and testing help ensure the treatment is working as expected and allow adjustments to be made if needed. This careful monitoring is designed to keep your dog as safe and comfortable as possible.
While heartworm treatment does carry some risks, your veterinary team is trained to manage those risks and guide you through each step. Many dogs complete treatment successfully and go on to live full, active lives.
After treatment is complete, ongoing heartworm prevention becomes especially important. Preventive medication helps protect your dog from future infection and provides peace of mind moving forward.
Preventing Heartworm Disease
The good news is that heartworm disease is highly preventable, and many dog owners are already doing the right things to protect their pets. With consistent care and guidance from your veterinarian, heartworm prevention becomes a simple part of your dog’s regular health routine.
Most heartworm preventive medications work by eliminating heartworm larvae before they have a chance to mature and cause damage. When given on schedule, these preventives are very effective and provide reliable protection for dogs of all breeds and lifestyles.
Heartworm prevention typically includes:
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Monthly heartworm preventive medication, given year-round as recommended by your veterinarian
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Regular veterinary checkups and testing, even for dogs on prevention
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Maintaining a consistent schedule, so doses are not missed or delayed
Because mosquitoes can be active year-round in many regions — and may even enter homes — skipping doses or taking seasonal breaks can leave dogs unprotected. Even a short lapse in prevention may allow infection to occur, which is why veterinarians strongly advise consistency.
For dog owners who are already giving heartworm prevention as directed, this routine is doing exactly what it is meant to do: keeping your dog safe. If a dose is accidentally missed or delayed, your veterinarian can help you decide the next best step.
Preventing heartworm disease not only protects your dog’s health, but also avoids the stress, risk, and cost associated with treatment. Staying on prevention allows dogs to live active, comfortable lives — and gives owners peace of mind knowing they are taking responsible, proactive care.
Your veterinarian is your best resource for choosing the right preventive product and schedule for your dog. With their guidance, heartworm prevention becomes a dependable safeguard rather than something to worry about.
Consistent prevention protects dogs from infection and avoids the risks associated with treatment.
When to See a Veterinarian
Contact your veterinarian if:
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Your dog shows symptoms such as coughing or fatigue
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A heartworm preventive dose is missed
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Your dog has not been tested recently
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You are unsure which prevention method is best
Early detection greatly improves outcomes.
A Reassuring Note for Dog Owners
Learning about heartworm disease can feel overwhelming, especially when your dog’s health is involved. The important thing to remember is that you are not alone, and help is always available. With today’s veterinary knowledge, heartworm disease can be prevented — and when it does occur, it can often be treated successfully with careful, guided care.
By staying informed, working closely with your veterinarian, and maintaining a consistent prevention routine, you are doing everything possible to protect your dog’s well-being. These small, steady steps add up to a healthier future and many more happy years together with your dog.
Heartworms and Other Dog Parasites
Heartworms are just one type of parasite that can affect dogs. Fleas, ticks, and intestinal parasites can also impact your dog’s health and require proper prevention and care.
Learning about all common dog parasites helps dog owners take a proactive approach to lifelong health.
Helpful Dog Health Resources
You may also find these guides useful:
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Dog Owner’s Library
A helpful collection of guides covering dog care, training, health, behavior, nutrition, and everyday challenges — designed to support dog owners at every stage of their dog’s life. -
Complete Guide to Dog Health & Wellness
An in-depth resource focused on common dog health topics, preventive care, symptoms, treatments, and wellness tips to help you keep your dog healthy from puppyhood through the senior years. -
Alphabetical Dog Diseases Dictionary
An easy-to-use A–Z reference explaining dog diseases, conditions, and health terms in clear language — helping dog owners quickly understand symptoms, causes, and care options.