[Vasovagal syndromes].

Most cases of dizziness or syncope referred to the emergency department or to services of internal medicine are caused by vasovagal syndromes. They comprise relative bradycardia with vasoplegia, the cardiovascular response to a neurological stimulus. It is possible to distinguish vagal or vasovagal syncope which is very common, the very stereotype reflex syncopes, carotid sinus hypersensitivity sometimes associated with sinus node dysfunction and borderline forms such as orthostatic sinus tachycardia and cerebrovascular syncope. The differential diagnosis is vast, from simple hysteria to severe cardiac disease. Tilt testing should be indicated for diagnosis of most cases of syncope with apparently normal hearts. Therapeutic abstention is the rule, providing certain preventive measures are taken, but, should treatment be necessary, cardiac pacing remains an exceptional modality in vasovagal syncope. Strict clinical and physiopathological studies are still required to determine the long-term prognosis and the underlying mechanisms of these syndromes.