Heartworm disease is a very serious canine disease, responsible for killing thousands of dogs each year. The canine heartworm lives as a parasite in the bloodstream, especially the heart, of a dog. It can affect the dog's heart and circulation, as well as its lungs, kidneys, and liver. If left untreated, it will eventually result in death. This serious disease, however, is completely preventable. Heartworm preventatives come in both liquid and tablet form, and should be given either daily or monthly, depending upon the drug being used. Because heartworms are spread by mosquitoes, it is especially important that a dog receive heartworm medication during the warmer months. A veterinarian can advise you as to the best heartworm preventive to use and the time of year it should be administered. Consult a local veterinarian for more information on preventing heartworms.