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Study reveals the pathomorphological findings of 6 dogs, 3 males and 3 females, diagnosed with Heartworm disease. By necropsies were found a total number of 144 adult stages (74 male and 70 female) of the nematode Dirofilaria immitis, located in a. pulmonalis, right ventricle and atrium and sulcus vena cavae. The gross pathology shows right-sided enlargement of the heart, dilated pulmonary arteries, and single petechial hemorrhages in the lungs. Histopathologically, degenerative changes in the pulmonary arteries, thickening of the pulmonary valves, interstitial reactions in the lungs and protein precipitates in the kidneys were found