Repolarization disorders leading to ventricular tachyarrhythmias are common causes of sudden cardiac death. Two of the disorders have been recently described at the molecular level revealing gene mutations: long QT syndrome, characterized by a prolonged QT interval corrected for heart rate and high incidence of malignant ventricular tachycardia, mainly torsade de pointes, and Brugada syndrome characterized by a ST segment elevation in the right precordial leads (V1-V3), right bundle branch block and idiopathic ventricular fibrillation. This review outlines current understanding of molecular genetic basis and pathophysiology of these diseases. On the basis of these repolarization disorders lay ion channel dysfunctions. The new discoveries may in the future allow a better diagnosis by genetic testing and raise the possibility of effective treatment by means of the gene-specific therapy.