Preface Heartworm revisited Since its foundation in 1974, the American Heart- worm Society has become the major source of up-to- date information on heartworm disease around the world. All the information presented in the triennial symposia was traditionally published as stand-alone books of proceedings. Since 2004, this has been changed, and in cooperation with Veterinary Para- sitology , we are now proud to present to you peer- reviewed formally printed versions of the material presented at the 2007 Symposium. This American Heartworm Society State of the Heartworm Symposium was held in conjunction with the annual meeting of the American Veterinary Medical Association held in July in Washington DC. During the American Heartworm Society Sympo- sium of 2004, we received revolutionary information of great value and use for the veterinary practitioner. Three years later at the 2007 symposium, many of the accepted paradigms in the heartworm and dog and cat relationship have been challenged and modified. A better understanding on how of Wolbachia participates in the disease as well as how the practitioner can better control the infection were some of the highlights. The misnomer of feline heartworm infection also became evident as the infection in cats is more a pulmonary pathological event. The sudden death syndrome, self- cure, diagnostic failures, and potential solutions were also highlighted. Heartworm Associated Respiratory Disease (HARD) was clearly discussed and the effects of pulmonary intravascular macrophages (PIMs) in this syndrome were elegantly described. Although it is not possible to mention every paper that has described new and innovative techniques and observations, we can proudly assert that the knowledge and understanding of heartworm in dogs and cats has advanced dramatically as a consequence of the triennial American Heartworm Society Symposium and the proceedings that are presented here. Jorge Guerrero* Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, 3800 Spruce Street, Philadelphia, PA 19104, USA Allan J. Paul Department of Veterinary Pathology, College of Veterinary Medicine, University of Illinois, Urbana, IL 61802, USA *Corresponding author E-mail address: jorgegu1@hotmail.com (J. Guerrero) www.elsevier.com/locate/vetpar Available online at www.sciencedirect.com Veterinary Parasitology 158 (2008) 163 0304-4017/$ – see front matter # 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.vetpar.2008.09.002