The congenital long QT syndrome (LQTS) is a leading cause of sudden death in the young. While most patients die during conditions of sympathetic activation, such as physical exercise or emotions, other die suddenly while at rest or during sleep. Several genes responsible for the disease have been identified. The most important genes encode ion channels involved in the control of ventricular repolarization. The currents involved are IKs, I Kr, and INa. Patients with mutations in the hERG gene form the LQT2 subgroup. This chapter reviews several critical clinical aspects focusing on differences between LQT2 patients and those from the other main subgroups (LQT1 and LQT3). Presentation and discussion of the different phenotypes is followed by a number of still unanswered questions related to specific features of the LQT2 patients.