Veterinarians practicing emergency medicine and/or working with exotic animals must be well versed in the pathophysiology of shock because many exotic pets present with an acute crisis or an acute manifestation of a chronic process causing poor organ perfusion. This article discusses the pathophysiology of shock and the systemic inflammatory response syndrome, which may lead to organ dysfunction, organ failure, sepsis, and death. The physiology of perfusion, perfusion measurements, categories of shock, and altered function of the immune system, gastrointestinal barrier, and coagulation system are discussed. Veterinarians providing emergency care to patients with shock must also be aware of comorbidities.