Syncope is a transient loss of consciousness secondary to inadequate cerebral perfusion with oxygenated blood. Syncope may be the clue to life-threatening cardiac diseases, including the long QT syndrome commonly misdiagnosed in children and adolescents as seizures or simple fainting. Postural hypotension is an important cause of syncope and must be quickly excluded. This chapter covers the causes of syncope, patient assessment, threat to life, neurocardiogenic syncope, long-QT syndrome, postural hypotension, diagnostic testing, and management. An obvious cardiac cause can be defined by a sound patient history, physical examination, electrocardiogram (ECG) and Holter monitoring. Neurocardiogenic syncope, simple faint (also called vasodepressor, vasovagal syncope, and reflex syncope) accounts for more than 30% of cases of syncope and must be excluded by a relevant history.