n 1  :  a filarial worm of the genus Dirofilaria (D. immitis) that is esp. common in warm regions, lives as an adult in the right heart esp. 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  2  :  infestation with or disease esp. of dogs caused by the heartworm, resulting typically in gasping, coughing, and nervous disorder, and when severe commonly leading to death .
 
 
 
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