Interceptor Spectrum protects your dog from deadly heartworm. Immature heartworm are spread to your dog when they are bitten by infected mosquitoes. When the heartworms mature, they live in the vessels of the heart and lungs, and can reach up to 30cm in length. If left untreated, heartworm disease causes heart failure and sadly death. Treatment for heartworm is dangerous and expensive, so prevention is essential. Unlike some other monthly heartworm treatments, Interceptor Spectrum also treats and controls tapeworm plus all major intestinal worms including roundworm, whipworm and hookworm.