The past 2 decades have witnessed the emergence of many disease states related to ion-channel disorders, the so-called “channelopathies,” usually associated with structurally normal hearts. The initial emphasis was directed toward the congenital long QT syndrome and the Brugada syndrome. Recently, the hereditary short QT syndrome has emerged as yet another rare channelopathy. This autosomal dominant syndrome can afflict infants, children, or young adults; often a remarkable family background of sudden cardiac death is elucidated. The electrocardiogram is characterized by a strikingly short QT interval (typically <320 milliseconds); virtual absence of the ST segment; and tall, peaked, narrow-based T waves. There is a marked propensity for paroxysmal atrial fibrillation, and increased risk for sudden cardiac death from ventricular tachyarrhythmias. At electrophysiology study, short atrial and ventricular refractory periods are found, with easily inducible atrial fibrillation and polymorphic ventricular tachycardia with programmed electrical stimulation. Gain-of-function mutations in 3 genes encoding potassium channels have been identified, which explain the abbreviated repolarization seen in this condition. The suggested treatment is an implantable cardioverter-defibrillator, though the possibilities of inappropriate shocks have caused some concern, especially in younger patients. The ability of quinidine and disopyramide to prolong the QT interval has the potential to be effective pharmacological therapy for patients with short QT syndrome, but awaits additional confirmatory clinical data.