Heartgard Plus is used in the prevention of heartworm infection and the control and treatment of various other worm infections. It kills the immature form of the heartworm (Dirofilaria immitis), which is transmitted by a mosquito. It is also used for the treatment and control of hookworms (Ancylostoma caninum, A. brasiliense, and Uncinaria stenocephala) and roundworms (ascarids – Toxocara canis, Toxascaris leonina). Heartgard Plus contains two active ingredients: ivermectin, which interferes with the parasite’s nerve transmission, causing paralysis and death of the immature heartworms (larvae), and pyrantel pamoate, which also interferes with the parasite’s nerve transmission, causing paralysis and death of intestinal worms.