A Siberian Husky from the Milan region was referred to the Clinic for clarification of a history of weight loss and rapid fatigue. On clinical examination increased vesicular sounds and dyspnea after physical excitement and effort were the only abnormal findings demonstrable. Radiologically demonstrated changes of the pulmonary arteries led to a tentative diagnosis of Dirofilariosis. The parasitological diagnosis based on serology and the morphology of microfilariae isolated from the blood indicated an infection by microfilariae and adult stages of Dirofilaria immitis. After premedication with Aspirin, the patient was treated against adult filariae with Caparsolate, and a month later with Ivermectin against the microfilariae. At the time of reexamination, 5 months after initiation of therapy, the dog was clinically healthy and free of any demonstrable infection with Dirofilaria. In a second, clinically normal Husky from the same kennel, isolated Dirofilaria repens microfilariae were demonstrated. This dog was not treated.