SEVERAL FORMS: Congenital long QT syndrome is a clinically (with and without deafness) and genetically (recessive or dominant autosomal inheritance) heterogeneous entity characterized by a long QT interval on the ECG associated with the risk of severe ventricular arrhythmia (torsade de pointes, ventricular fibrillation) and subsequent syncope or sudden death.This rare familial syndrome is transmitted by different modes of inheritance and occurs in subjects with a morphologically normal heart. The severity of the prognosis justifies screening tests. The genetic origin of the disease has been confirmed and at least 5 loci and 4 genes have been identified, giving a perfect illustration of adrenergic ventricular rhythm disorders. Beta-blockers are used as first line treatment in symptomatic patients.All drugs favoring QT interval lengthening are contraindicated in all subjects with a genetic anomaly. All members of the direct family must have a Holter recording and genotype in order to identify mutation carriers or asymptomatic patients.