Heartgard Plus Chewables etc. (ivermectin/pyrantel pamoate) contain a broad-spectrum antiparasitic drug (ivermectin) to kill the immature form of the heartworm (Dirofilaria immitis). They also contain an antihelminthic medication (pyrantel pamoate) to prevent intestinal parasites like roundworms and hookworms.
Higher dosages of ivermectin are required to treat ear mites and demodectic and sarcoptic mange.
(Certain dog breeds are genetically hypersensitive to ivermectin. These breeds include the Australian Shepherd, German Shepherd, Shetland Sheepdogs and Collies. A veterinarian should also be consulted before beginning a treatment involving ivermectin.