Vulnerable window of conduction block in host-donor strands as a function of RT profile shape. A-C, Relationship between vulnerable time window for S2 block and shape parameters of RT profile, namely: height (A), width (B), and maximum gradient (C); linear regression fit lines are shown only for statistically significant correlations (see Table II in onlineonly Data Supplement). D, Average vulnerable time windows for S2 block in host-donor strands without or with BaCl2 application. ***P<0.001, n=16–21 per group.