A, Comparison of incidence of post (3 day)-CS AF between patients not treated (, −BB, n=13/48) and treated (, +BB, n=13/99), respectively, for >7 days pre-CS with a beta-blocker. Asterisk denotes P<0.05 between groups. B, Comparison of magnitude of increase in mean pre-CS atrial cellular effective refractory period (ERP) associated with pre-CS treatment (>7 days) of patients with a beta-blocker, between those in post-CS sinus rhythm (□; patient n: −BB=21; +BB=43) and post (3 day)-CS AF (■; patient n: −BB=4; +BB=5). †s denote P<0.05 for the increase in ERP associated with pre-CS β-blockade within each group.