What Are the Symptoms of Heartworm in Dogs?

Heartworm symptoms in dogs can be hidden, as heartworm disease is one of the few parasitic infections where a dog can look healthy for months while damage is already building in the heart and lungs. This guide from Tree Pet Veterinary explains what heartworm does and how the signs change as it progresses.

What Is Heartworm Disease in Dogs?

Heartworm is caused by a parasitic worm called Dirofilaria immitis. Adult worms live in the pulmonary arteries, the vessels carrying blood from the heart to the lungs, and in severe cases in the heart itself. It spreads by mosquito bite, not from dog to dog.

Larvae take six to seven months to mature, and adult worms survive for years. While they do, they inflame the artery walls and force the heart to pump against rising pressure. To guarantee your dog’s safety, feel free to visit our clinic and check our expert solutions for pet deworming in Sharjah, as much of the harm from heartworms comes from that slow strain, not the worms themselves. 

What Are the Symptoms of Heartworm in Dogs?

Symptoms follow the disease rather than appearing at once, and the stage changes both the urgency and the plan.

Early Signs

In the first months there is often nothing to see. Early signs are easy to blame on age, heat or weight:

• An occasional dry cough, often after exercise

• Slightly less enthusiasm for walks or play

• Taking longer to recover after activity

More Advanced Symptoms

As worm burden and lung damage increase, the picture becomes clearer:

• A persistent cough that no longer settles with rest

• Clear exercise intolerance, such as tiring on short walks or refusing stairs

• Reduced appetite and gradual weight loss

• Faster or more laboured breathing

Emergency Warning Signs

Some signs mean a dog needs seeing the same day:

• Collapse, fainting or sudden severe weakness

• Open-mouth breathing at rest, or pale, grey or blue gums

• A visibly swollen or fluid-filled abdomen

• Dark red or brown urine, or coughing up blood

A swollen abdomen reflects fluid building up as the right side of the heart begins to fail, and any of these signs warrants emergency veterinary care rather than waiting for the next available appointment.

Can Dogs Have Heartworms Without Symptoms?

Yes, and it is the most important thing to understand about the disease. Dogs with few worms may never show obvious signs, and quiet or indoor dogs are rarely active enough for exercise intolerance to appear.

How Is Heartworm Diagnosed?

Diagnosis starts with a blood test for antigen, a protein released by adult female worms, usually with a test for larvae in the blood, run as part of wider blood and laboratory testing at Tree Pet Veterinary.

Timing matters: because larvae need about six months to mature, a test run too soon can read negative in a dog that is infected. If it is positive, chest radiographs and sometimes a heart ultrasound show how much damage has occurred, which decides the treatment approach.

How to Treat Heartworm in Dogs

When owners ask how to treat heartworm in dogs, the answer begins with what it is not: there is no safe home remedy, and no over-the-counter product clears an adult infection. Treatment is directed entirely by a veterinarian:

• Confirm and stage first; advanced cases may need supportive care before worms are killed

• Prescription medication to kill adult worms, given in stages over weeks

• Strict exercise restriction, which is not optional: dying worms break apart and can block lung vessels

• Follow-up testing months later to confirm the infection has cleared

Can Heartworm Be Prevented?

Yes, and prevention is far simpler than treatment. Preventive medication is given on a regular schedule, monthly in most products, and clears larvae before they mature. A dog of unknown status should be tested first: giving a preventive to a dog already carrying circulating larvae can trigger a serious reaction. Prevention is not treatment and will not remove established adult worms.

Mosquito exposure is why this matters in the UAE. Standing water, irrigation and humidity all support mosquito activity, so prevention is worth discussing with your vet rather than assuming an indoor dog is safe.

Heartworm vs. Intestinal Worms

These two are often confused, and the confusion can be costly.

A routine intestinal dewormer does not protect against heartworm unless specifically labelled for it, and many are not. If you follow a deworming schedule, or use our pet deworming service, check with your vet whether it covers heartworm too.

When Should You Take Your Dog to a Veterinarian?

Book an appointment for a cough lasting more than a few days, reduced stamina, unexplained weight loss, or any change in breathing. Owners can arrange an examination at our Veterinary Clinic in Sharjah and should go the same day for collapse, breathing distress, or pale gums. 

Final Thoughts

Heartworm is quiet before it is serious, and a cough or a few lost kilos are easy to explain away. If your dog shows any of these signs, or you are unsure whether its prevention covers heartworm, book an examination and ask.

Frequently Asked Questions

What are the first signs of heartworm in dogs?
Usually subtle: an occasional cough after exercise, less interest in walks, or taking longer to recover. Many show nothing early on.

Can a dog have heartworm without symptoms?
Yes. A dog can carry adult worms for a year or more without obvious signs, especially if the burden is small.

How is heartworm diagnosed in dogs?
A blood test detecting antigen from adult female worms, usually with a test for circulating larvae. Positive results are followed by imaging.

How to treat heartworm in dogs?
Only under veterinary direction: staging, prescription medication over weeks, strict exercise restriction, and follow-up testing. There is no safe home treatment.

Can heartworm be prevented?
Yes, with regular preventive medication prescribed by your vet. A dog of unknown status should be tested first.

Can heartworm be fatal in dogs?
It can be. Untreated infections can lead to heart failure, and sudden obstruction of blood flow through the heart is life-threatening.