Heartworm disease is probably the most well-known disease of dogs, and its epidemiology is being recorded in those countries in which the disease is routinely treated in the domestic dog. It is hoped that this text will be of benefit to us all and that our understanding of this disease will continue to grow and so enable us to resolve some of the exsiting problems associated with the treatment of this disease. To this end, the book aims to project some hypotheses in different areas that, while unproven, seem to be the most probable, based on our current knowledge.