Women are known to be more susceptible to long-QT syndrome and related arrhythmias, namely torsades de pointes [1], also in relation to use of various drugs, both cardiac and noncardiac (for a review see Ref. [2]). On the other hand, the incidence of Brugada syndrome and related arrhythmias is higher in men [3]. Sex differences in the susceptibility to arrhythmias were also demonstrated in experiments on various animal species, including rabbit [4] or dog [5]. Some of the sex-specific features of cardiac electrophysiology underlying the varying susceptibility of men and women to various types of arrhythmias have been already revealed, as will be discussed in this chapter. Gaps in the knowledge will be identified.