Heartgard Plus Chewables are for use in dogs to prevent canine heartworm disease by eliminating the tissue stage of heartworm larvae for a month (30 days) after infection and for the treatment and control of ascarids and hookworms . Heartgard Plus should be administered orally at monthly intervals. Heartgard Plus is recommended for dogs 6 weeks of age and older. Available in three color coded dosages. Made by Merial.