Despite sharing strong electrical instability, two distinct phenotypes can be identified in carriers of CaM mutations: the long QT syndrome (LQTS) (9, 73), characterized by prolongation of repolarization, and catecholamine-induced ventricular tachycardia (CPVT), characterized instead by exercise-induced ventricular arrhythmias (74). This evidence concerns the gene CALM1 and catecholaminergic polymorphic ventricular tachycardia.