Chest pain is the most important chief complaint encountered by the emergency physician. There are numerous life-threatening causes of chest pain, the most important of which is ischemic heart disease. Ischemic heart disease is the number one cause of death in the United States and a leading cause of malpractice litigation against emergency physicians. In addition, patients with several other life-threatening conditions initially complain of chest pain. As such, differentiation between life-threatening and non–life-threatening causes of chest pain is a key aspect of the practice of emergency medicine.