A, the numbers of induced VF episodes were similar between females and males at baseline, during isoproterenol and after washout. After apamin, however, the numbers of induced VF episodes became significantly lower in females than in males. VF inductions were attempted 10 times at baseline and after each treatment. B, representative phase maps of the first 100 ms of VF after the onset at baseline, after isoproterenol, after apamin and after washout in females (upper panel) and males (bottom panel) (Protocol VII). Compared with baseline, isoproterenol markedly increased the numbers of phase singularities (PSs, black arrowhead) in both groups. Apamin prominently decreased PSs in females, but the effect was less prominent in males. After washout, the numbers of PSs in all three groups were similar to those at baseline. C, the numbers of PSs were similar between sexes at baseline, after isoproterenol and after washout. After apamin, however, the numbers of PSs became significantly lower in females than in males. D, VF dominant frequencies were similar between sexes at baseline. After isoproterenol, dominant frequency became significantly higher in females than in males. Apamin eliminated the isoproterenol‐induced differences in dominant frequency between sexes. After washout, the dominant frequencies remained similar in females and males. *P < 0.05 by two‐way ANOVA with Sidak's post hoc test. [Color figure can be viewed at http://wileyonlinelibrary.com]