Why do dogs die from heartworm?

Heart worm infestation doesn't manifest in a dog until it is often too late, whereas other types of worms found in the digestive tract can cause loss of weight and are usually seen in a dog's stools. Only a blood workup by a vet can detect heart worms, which is a gradual killer that compresses a dog's heart and the worms feed directly off the blood. A dog can appear perfectly healthy for months but will eventually (once the cardiovascular system is overstressed) begin showing signs of inactivity and a lot of panting/shortness of breath. Preventive medicines (e.g., Heartgard) should be given at regular intervals to any dog that is a loved member of the family.