Supplementary Video 1A. Simultaneous Vm, CaT, and LCR high-speed recordings in an isolated rabbit SAN cell, imaged using both Fluo-4 AM Calcium indicator and patch-clamp recording. Subcellular LCRs are visible before and ater the appearance of an APCT. Adapted from (Tagirova Sireko et al., 2021). Supplementary Video 1B. Simultaneous Vm, CaT, and LCR high-speed recordings in an isolated, previously arrested human SAN cell, imaged using both Fluo-4 AM Calcium indicator and patch-clamp recording. APCTs and spntaneous APs occurred after B-AR activation 1uM isoproterenol. Adapted from (Tsutsui et al., 2018).