6 Signs Your Dog Might Have Heartworm

April is National Heartworm Awareness Month, and it’s a good time to begin watching out for the symptoms of heartworm in your dog. As the temperature starts to warm up and the weather gets wetter, mosquitoes start to hatch and buzz around, spreading itchy bites all over the place. But mosquitoes are more than just a nuisance. They are transmitters of heartworm. If you and your dog have spent time in an area where mosquitoes are prevalent, keep an eye out for these 6 symptoms that are signs your dog might be infected with heartworm.

1. Coughing

A Jack Russell Terrier coughs.

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Dogs in the early stages of heartworm might exhibit no symptoms, or they might only have a mild cough. Even with a physical at the vet, it may be difficult to detect, as blood tests may come back negative. Keep an eye on the cough, and if it gets worse, take a trip to the veterinarian.

2. Fatigue

A shaggy black dog lies on his side.

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If your dog seems more tired than usual after exercise, it may be a sign that a heartworm infection is progressing. Coughing gets worse at this stage, and your dog may sleep too much or refuse to exercise at all. By this point, a blood test should be able to detect heartworm with some certainty.

3. Breathing Difficulties

A dog lies on a vet's table for an x-ray.

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As the infection spreads to the blood stream and the cough gets worse, your dog may have trouble getting enough air. The coughing and fatigue will get worse, as well, and your dog may cough up blood or have nosebleeds. At this point, the heartworm should be plainly visible by x-ray.

4. Weight Loss

A black Great Dane puppy refuses to eat.

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Without treatment, symptoms will start to take a greater, more permanent toll on the body. Loss of appetite will start to affect your dog’s weight. If your dog is refusing to eat and losing an unusual amount of weight, it’s likely that the disease has moved on to a fairly late stage.

5. Bulging Chest

A vet listens to a dog's chest with a stethoscope.

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As your dog loses weight, the chest may start to bulge. This can also be caused by a buildup of fluid in the chest in response to the parasite. If you haven’t already done so, seek the help of a veterinarian. The disease is definitely in a late stage at this point.

6. Collapsing

A dog lies on a wood floor with a blue background.

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When heartworm spreads in the heart and bloodstream, eventually blood flow becomes blocked. This can lead to shock or destruction of red blood cells, and your dog will start collapsing. Seizures, blindness, and lameness can result in cases where the parasites move to the brain. If the disease goes untreated from here, it can be fatal.

If you see these symptoms, do not begin treatment of your dog on your own. Some treatments at this point can cause death if a dog already has the disease. Consult your veterinarian. Preventative medication and yearly exams are the best way to stop heartworm. 

Have you kept your dog’s heartworm treatment up-to-date? What preventative measures do you take? Let us know in the comments below.