Extended Data Fig. 6: Small-scale signal conduction within the cardiac tissue by the 128-FET array.

The 128-FET array is classified into 40 units, where each arm has five units. Each unit is labelled by the combination of the located arm name (for example, ‘A’), the loop number (for example, ‘1’), and the relative location (for example, ‘a’). In each unit, the FETs are labelled in i, ii, iii, and iv. Within each unit, intercellular signal conductions via gap junctions in neighboring cells are analyzed, and the latencies are denoted in the heatmaps. The signal conduction velocity inside each unit can be calculated. For instance, in E2b, the signal transmits 70 μm from E2iv to E2vi in 5 ms. By analyzing all signal conductions within each unit, we calculated the small-scale conduction velocity (Supplementary Table 5), whose average and standard deviation are 18.8 ± 7.5 μm·ms⁻¹, which are consistent with previously reported values. The triangle for each unit indicates the selected FET that has the earliest spike within that unit. We use the selected FET in each unit as the reference point to calculate the signal conduction velocities among different units. NaN: Not a number, meaning no cellular signal was recorded.