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Echocardiography, vital signs, microfilaremia, and blood chemistry of 12 Jindo dogs naturally infected with canine heartworms (Dirofilaria immitis) were analysed and compared with those of 5 uninfected control Jindo dogs. Nine of the twelve infected dogs contained microfiaria in the peripheral blood, whereas the presence of adult heartworms in the pulmonary arteries and/or in the heart was detected from four dogs by echocardiography. Among the four echocardiography-positive dogs, two dogs also displayed evidence of heartworms in the right ventricle by echocardiography. Upon necropsy, a total of 547 adult worms was collected from the 12 infected dogs (av = 45.6, range = 9-166). Dogs with positive echocardiograpic images of heartworms contained 48, 74, 104 and 166 adult worms in the heart, pulmonary arteries and/or in the caudal vena cava (av. 98.0), whereas 9 to 39 worms (av. 19.4) were collected from those organs of dogs with negative echocardiography. Most heartworms were found in the right ventricle (438, 80%) at necropsy, whereas relatively fewer worms were found in the pulmonary arteries (96, 17.6%), and in the caudal vena cava (13, 2.4%). The necropsy findings on the location of adult worms significantly differed from the results of echocardiographic analysis in which the right ventricle of most dogs did not show the presence of heartworms. These results indicated that the adult heartworms had been located in the terminal branches of the pulmonary arteries when the host was alive, but the worms moved toward the right ventricle shortly after the heart of the infected dogs stopped beating. Microfilaremia in the peripheral blood was the highest in the blood samples collected at 10 pm. However, the correlation between the number of microfilaria and of adult worms was not observed. Clinical and vital signs of infected dogs did not show any significant difference before and after a 30 minute-exercise at 5 ㎞/hr compared to those of uninfected control dogs.
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