A heartworm cough is typically dry, harsh, and persistent, often compared to the sound of a goose honking. It doesn’t produce mucus, and it won’t go away on its own or improve with rest. Unlike a brief cough from dust or excitement, this cough tends to come in fits triggered by physical activity or eating, and it gets worse over weeks and months as the disease progresses.
What the Cough Sounds Like
The most distinctive feature is a dry, hacking quality. Some veterinarians describe it as a honking sound, similar to a goose. It’s forceful and repetitive, not the soft, wet cough you might hear with a respiratory infection. Dogs with heartworm disease often cough in bouts rather than producing a single cough here and there, and even mild exertion like a short walk or climbing stairs can set off a coughing episode.
In early stages, the cough may be occasional and easy to dismiss. But because the underlying cause is worms living in the blood vessels of the lungs, the irritation is constant and progressive. A cough that started after a run might eventually show up at rest, during meals, or while the dog is lying down.
Why Heartworms Cause a Cough
Heartworms don’t live in the lungs directly. They lodge in the pulmonary arteries, the large blood vessels that carry blood from the heart to the lungs. Their presence triggers intense inflammation in those vessels and in the surrounding lung tissue. The body’s immune cells swarm the area, and the resulting swelling narrows the airways and irritates the bronchial passages. This creates the persistent cough reflex.
When heartworms die, they release bacteria called Wolbachia that live inside them. The immune system reacts to these bacteria as well, causing further lung inflammation. This is why the cough can actually worsen during certain phases of infection, even during treatment, as dying worms provoke a stronger inflammatory response than living ones.
How It Differs From Kennel Cough
Kennel cough can sound remarkably similar, also producing a harsh, honking cough. The key difference is timing and duration. Kennel cough is a short-term infection that typically resolves within one to three weeks, often with antibiotics. A heartworm cough doesn’t resolve. It persists for weeks, then months, gradually worsening.
Context matters too. Kennel cough usually appears after exposure to other dogs, such as a boarding facility, dog park, or grooming salon. A heartworm cough develops without any obvious exposure event and is more likely to flare with exercise. If your dog’s cough lasts beyond two to three weeks or gets worse with activity rather than better with rest, heartworm disease becomes a real concern.
When the Cough Appears in the Disease
Heartworm disease progresses through stages, and the cough doesn’t show up immediately. After a mosquito bite transmits heartworm larvae, it takes roughly six months for the worms to mature and reach the pulmonary arteries. During this early period, most dogs show no symptoms at all.
The FDA classifies heartworm disease into stages based on severity. In Class 2, dogs develop an occasional cough and tire more easily after moderate activity. By Class 3, the cough becomes persistent and is joined by more serious signs: a visibly sickly appearance, fatigue after even mild activity, difficulty breathing, and early signs of heart failure. By the time a cough is noticeable, the disease has already been progressing silently for months.
Other Signs That Accompany the Cough
A heartworm cough rarely appears in isolation. Watch for these alongside it:
- Exercise intolerance: Your dog tires quickly on walks they used to handle easily, or seems winded after brief play.
- Labored breathing: Faster or heavier breathing, even at rest.
- Lethargy: Less interest in play, walks, or normal activity.
- Weight loss: Gradual loss of body condition despite normal eating.
- Swollen belly: In advanced cases, fluid can accumulate in the abdomen due to heart failure.
If you’re noticing two or more of these alongside a dry, persistent cough, heartworm testing is a straightforward next step. A simple blood test can detect heartworm proteins, and veterinarians recommend annual screening even for dogs on preventive medication.
Heartworm Cough in Cats
Cats with heartworm disease present very differently. Rather than the classic honking cough seen in dogs, cats develop a condition called Heartworm Associated Respiratory Disease, or HARD. This looks almost identical to feline asthma: coughing, wheezing, increased breathing rate, and episodes of respiratory distress. Because of this overlap, heartworm disease in cats is frequently misdiagnosed as asthma or bronchitis.
The underlying process is different too. In cats, immature heartworms arrive in the pulmonary arteries around 70 to 90 days after infection and provoke a severe inflammatory reaction in the lungs, affecting the bronchial passages, the tissue between the air sacs, and the small arteries. Most of the worms die before reaching maturity, but the lung damage from their arrival and death can persist for months. Cats may also show vomiting, decreased appetite, weight loss, and reduced activity alongside any respiratory signs.
Ferrets are also susceptible and show similar signs to dogs: coughing, difficulty breathing, weakness, and decreased activity. Because ferrets are small, even one or two adult heartworms can cause heart failure.
Getting a Diagnosis
If your dog has a persistent dry cough, the standard diagnostic approach is a blood test that checks for heartworm antigens (proteins shed by adult female worms). The American Heartworm Society recommends combining this with a separate test that looks for microfilariae, the microscopic larvae that circulate in the bloodstream. Using both tests together catches cases that either test alone might miss.
One important nuance: in some infections, the immune system can mask heartworm proteins in the blood by binding to them, creating a false negative result. If heartworm is still suspected despite a negative test, a veterinarian can heat-treat the blood sample to break apart these protein complexes and reveal a more accurate result. This is particularly relevant for dogs with a classic heartworm cough but no positive test on the first try.