These are roundworms (Toxocara canis, Toxascaris leonina), hookworms (Ancylostoma caninum), whipworms (Trichuris vulpis), tapeworms (Dipylidium caninum), and heartworms (Dirofilaria immitis). All these worms except heartworms live in the intestines of dogs. Heartworms, as the name suggests, live within the heart and the blood vessels.