Optical mapping of samples at a stimulation frequency of 60bpm and 100bpm. Figures (A–F) show the activation maps (sample size - 15 mm) for the calcium wave recorded during optical mapping for 2 stimulation frequencies: 60bpm (or less) and 100bpm. Under each map records of the intensity of the calcium signal in two different areas are given. (G) Graph of wave conduction velocities measured on different days of differentiation. (H) Values of the correlation for each sample. On both graphs, blue dots represent control samples, and red and green - transferred ones.