Gender differences play a major role in the manifestation of cardiovascular disease including cardiac arrhythmias. In particular, female sex is an independent risk factor for development of torsade de pointes (TdP) arrhythmias not only in congenital long QT syndromes but also in acquired long QT syndromes which occur as adverse effects of existing drugs. Recent clinical and experimental studies suggest that the gender differences may stem, at least in part, from gender differences in cardiac repolarization process, that is longer rate-corrected QT (QT(C)) interval in women than in men. In women, QT(C) interval and arrhythmic risks in TdP alter cyclically during menstrual cycle, suggesting a critical role of female sex hormones in cardiac repolarization process. These gender differences in fundamental cardiac electrophysiology result from variable ion channel expression and diverse sex hormonal regulation via long term genomic and acute non-genomic pathways, and sex differences in drug responses and metabolisms. In particular, non-genomic actions of testosterone and progesterone on cardiac ion channels likely to contribute to the gender differences in cardiac repolarization processes.