: a filarial worm of the genus Dirofilaria (D. immitis) that is especially common in warm regions, lives as an adult in the right heart especially of dogs, and discharges active larvae into the circulating blood whence they may be picked up by mosquitoes and transmitted to other hosts and that may infect humans causing local pulmonary infarction but does not achieve sexual maturity in the human organism
: infestation with or disease especially of dogs caused by the heartworm, resulting typically in gasping, coughing, and nervous disorder, and when severe commonly leading to death
Species (Dirofilaria immitis) of filarial worm that parasitizes mammals, especially dogs. Up to 500 adult heartworms, which can grow to 6–12 in. (15–30 cm) long, live in the dog's heart, and the microfilariae (embryonic larvae) pass into the blood. Mosquitoes transfer infested blood from dog to dog. Both adult and larval heartworms tax the heart and restrict blood flow to the lungs, kidneys, and liver. By the time visible symptoms (chronic cough, labored breathing, listlessness, heart failure) develop, it may be too late for treatment. Preventive medicines and treatments, including surgery, exist.