Two Jindo dogs which show clinical signs of anorexia, weakness and exercise intolerance, were referred, and diagnosed as dirofilariasis by hematology, blood chemistry and ultrasonography. In hematology and blood chemistry, the presence of microfilariae in the blood, anemia, leukocytosis, hemoglobinuria and jaundice were revealed. In ultrasonography, heartworms were found in the right ventricle artery and pulmonary artery as structures of hyperechoic dots or streaks. In autopsy, forty odd and fifty odd of heartworms at dog 1 and dog 2, were ascertained respectively in the right ventricle and pulmonary artery.