April has become heartworm awareness month in North America because of the exposure rate increase around this time of year. It is important that you keep up with your dog’s prevention medication and to schedule a checkup. If your dog does contract heartworms disease, the earlier the diagnosis, the better chances of recovery.

Signs of heartworm in dogs

Heartworm disease causes two main issues, first damages to the arteries in the lungs and the second is obstruction of blood flow as a result of inflammation. There are no physical symptoms when the dog becomes inflected by the heartworm initially. Within days, the artery lining is damaged. Their body responds by inducing inflammation of the artery.

Overtime the vessels in the arteries become tortuous and dilated. Blood clots and aneurysms often become a side effect. The blood then reroutes to non-worm burdened areas. This blockage causes fluid to accumulate around these blood vessels in the lungs, making it harder for the lungs to oxygenate the blood.

The physical signs begin when the dog begins coughing and shows signs of exercise intolerance, nosebleeds, and shortness of breath. Pneumonia can also develop due to the increase of fluid around the lungs. If left untreated, more worms can arrive and cause even more damage eventually leading to heart failure.   

Treatment involves two basic areas:

  1.  Patient evaluation and stabilization for treatment procedure.
  2.  Elimination of all forms of the heartworm parasite.


It is much easier to prevent heartworms than to treat them. The most common preventatives on the market kill the immature heartworm larvae before they molt. As long as your dog is given his medication each month it is effective at preventing this disease.

The choice of which preventative to use will be determined by a discussion with your veterinarian and what is best for your pet. Ideally, puppies are started on monthly heartworm preventatives by 8 weeks of age. They should have a heartworm blood test at around 7 months of age and then be retested on an annual basis or according to the veterinarian’s recommendations.

The latest recommendation by the American Heartworm Society is once every 2-3 years in dogs that NEVER miss a dose of preventative. Any missed preventative doses should be communicated to your veterinarian and re-testing should be scheduled accordingly.