When a dog is first infested with heartworm there are no visible or detectable signs. Even a blood test will not detect heartworms initially. Remember the current heartworm test only can detect heartworms at the adult stage (6 months or older). The changes in dogs begin during the final stage of the adolescent heartworm; when that heartworm arrives in the right ventricle of the heart and neighboring blood vessels.
Within days, the dog’s artery lining is damaged & the blood vessels dilate. Heartworms cause damage at a rate faster than the body can heal causing inflammation, blood vessel obstruction, & accumulation of fluid in the lungs reducing the effectiveness of the lungs’ ability to oxygenate the blood.
At this point, you may see your pet begin to cough, display exercise intolerance, nosebleeds & shortness of breath, as well as pneumonia due to lung inflammation. Blood vessels are now blocked & lung tissue is damaged which can cause heart failure.
Often there will be no signs of heart disease and your pet may collapse. When fainting and collapse does occur, it is accompanied by severe shock, red blood cell destruction and often death within 1-2 days.