The Life-Threatening Nature of Heartworm Disease in Dogs
Heartworm disease happens when your dog is infected by a parasite called Dirofilaria immitis. These long, spaghetti-like worms grow inside your dog’s heart, lungs, and nearby blood vessels.
Some heartworms can grow up to 12 inches long. In serious cases, dogs may carry over 200 worms at once. As they grow, they block blood flow, strain the heart, and damage the lungs. Without treatment, heartworm disease can become life-threatening.
Even more concerning, the early stages usually show no symptoms. That’s why it often goes unnoticed until major harm is done.
How Mosquitoes Transmit Heartworms to Dogs
Heartworms don’t spread directly from dog to dog. They need mosquitoes to move from one host to another.
Here’s how it works: When a mosquito bites an infected dog, it picks up baby worms called microfilariae. Over the next 10–14 days, those babies grow into larvae inside the mosquito. Then, when the mosquito bites another dog, it injects the larvae into the skin. The larvae travel through the body and grow into adult worms over six months.
This cycle can happen anywhere mosquitoes are present—even indoors. That’s why heartworm prevention and treatment for dogs should never be seasonal or location-based. It’s a year-round concern.
Understanding how heartworms work is the first step in protecting your dog. Prevention is not just easier—it could save your dog’s life.
Why Year-Round Heartworm Prevention for Dogs Is Critical
The Dangers of Untreated Heartworm Infection in Dogs
Heartworm disease is dangerous because it hides quietly at first. Your dog may seem perfectly healthy in the early stages. But inside, the worms are growing and damaging the heart, lungs, and blood vessels.
As the infection progresses, it becomes much harder to treat. Dogs with heartworms can develop heart failure, lung disease, and permanent organ damage. In the worst cases, heartworms can cause sudden collapse or death.
Treatment is possible—but it’s tough. It involves multiple vet visits, long rest periods, and strict activity restrictions. Some dogs don’t survive the process. That’s why prevention isn’t just better—it’s critical.
Recognizing the Symptoms of Heartworm Disease in Dogs
By the time symptoms appear, your dog may already have significant internal damage. Common signs include a persistent cough, tiredness after light activity, and loss of appetite. You might also notice weight loss, or a swollen belly from fluid buildup.
In advanced cases, dogs may suffer from caval syndrome, a deadly complication where heartworms block blood flow. Symptoms can include collapse, labored breathing, and dark-colored urine—a medical emergency.
If your dog shows any of these signs, contact your vet immediately. But remember: many infected dogs don’t show symptoms until it’s serious. That’s why consistent prevention and regular testing are essential parts of heartworm prevention and treatment for dogs.
Heartworm Prevention Tips Every Dog Owner Should Follow
How to Use Heartworm Preventives Safely and Effectively
The best way to protect your dog from heartworms is through consistent, vet-recommended preventives. Start giving preventives at 6 to 8 weeks of age, before your puppy is exposed to mosquitoes. These medications come in different forms—chewables, topicals, and long-lasting injections—so you can choose what works best for your lifestyle.
Stick to a regular schedule. Most preventives are given monthly, and skipping even one dose can leave your dog unprotected. Brands like HeartGard30® PLUS and NexGard SPECTRA® are widely trusted and easy to use.
Keep up the routine all year long, not just in summer. Mosquitoes can survive in warmer homes or unexpected weather patterns. Heartworm prevention and treatment for dogs only works when it’s consistent. Even one missed dose can make a difference.
Why Annual Heartworm Testing Is Essential for Dogs
Testing plays a big role in keeping your dog safe. If your dog is over 7 months old, your vet will likely test for heartworms before starting prevention. After beginning, your dog should be retested at 6 months and 12 months, then once every year.
Why test even if you’re giving preventives? Because no method is perfect. Dogs may spit out a pill without you noticing, or a dose might not be absorbed properly. Regular testing catches any problems early—before symptoms or damage begin.
Testing + prevention is the gold standard. It’s the best defense against a disease that hides until it’s too late.
How Vets Diagnose and Treat Heartworm in Dogs
Blood Tests and Imaging Used to Diagnose Heartworm Disease
Diagnosing heartworm disease starts with a blood test. Your vet will check for a substance made by adult female worms—this is called an antigen test. If it’s positive, they may also look for baby worms in the bloodstream using a microfilariae test.
To understand how advanced the disease is, your vet may recommend chest X-rays or ultrasounds. These imaging tools help reveal how much damage the heart and lungs have suffered and guide the best treatment plan.
Step-by-Step Overview of Heartworm Treatment Protocol
Once the diagnosis is confirmed, the first step is rest. Even if your dog seems fine, physical activity can make things worse. Limiting movement reduces strain on the heart and helps prevent complications.
If your dog is showing symptoms, your vet will work to stabilize their condition before beginning treatment. This might involve medication to support breathing or reduce inflammation.
Next comes the adulticide treatment—a medication called melarsomine, given by injection. Some dogs receive two injections, while others—especially those with heavy infections—may get a split-dose protocol to lower risk.
After killing the adult worms, your dog will need treatment to remove the microfilariae still in the bloodstream. A topical solution like Advantage Multi® is often used.
Follow-up testing is essential. Your vet will test again in 6 to 9 months to confirm the heartworms are completely gone.
Potential Risks and Complications During Heartworm Treatment
Heartworm treatment is effective, but it’s not without risks. When worms die, they can break apart and block small blood vessels in the lungs. This is called thromboembolism, and it can be very dangerous.
Strict rest is the best way to reduce this risk. Your dog may need to be kept calm and quiet for weeks or even months.
In very severe cases, surgery or long-term care may be needed. But with careful planning and follow-up, heartworm prevention and treatment for dogs can lead to full recovery—even after infection.
Always talk to your vet about the best path forward for your dog. They’ll help you every step of the way.
Final Thoughts on Protecting Your Dog from Heartworm
Heartworm disease is deadly—but it’s also 100% preventable. By keeping your dog on a year-round preventive schedule and testing annually, you can avoid the pain, risk, and high cost of treatment.
Preventatives are far safer and more affordable than dealing with an active infection. They offer peace of mind and real protection, especially when paired with consistent vet checkups.
Testing and prevention should be part of your dog’s life—forever. Even one missed dose or unnoticed failure can leave your pet exposed. That’s why it’s so important to work with your veterinarian to choose the right product and schedule.
By understanding the risks and acting early, you’re taking a powerful step toward total heartworm prevention and treatment for dogs in your care.
Talk to your veterinarian today to start or update your dog’s heartworm prevention plan and schedule annual testing to keep your pet protected year-round.