The congenital long QT syndrome (LQTS) is a hereditary disorder characterized by a prolonged QT interval and a polymorphic ventricular tachycardia, known as torsade de pointes (TdP), leading to severe cardiac events such as syncope and/or sudden cardiac death. Molecular genetic studies have revealed a total of eight forms of congenital LQTS caused by mutations in genes of the potassium, sodium and calcium channels or membrane adapter located on chromosomes 3, 4, 7, 11, 12, 17 and 21. Genotype-phenotype correlation in clinical and experimental studies has been investigated in detail in the LQT1, LQT2 and LQT3 syndromes which constitute more than 90% of genotyped patients with LQTS, enabling us to stratify risk and to effectively treat genotyped patients.