Fig. 4.

Characterizations of the beating of representative human heart organoids. (A) hHOs beating characterized by OCT. During contraction, the bottom chamber shrank, and the valve-like structure (indicated by the red arrow) switched to a closed state. Recording of the hHO beating is shown in supplementary video 5. (B) hHOs beating characterized by fluorescence imaging of GCaMP6f (Chen et al., 2013; Huebsch et al., 2015). For panel A and B, 6 representative frames within the same beating cycle were taken from the recordings. All frames were time stamped. The circular arrows indicate the time sequence of each frame group. Scale bars: 200 μm. (C) Traces of hHOs beating. The blue traces on the left represent changes in the height of the chamber, measured from the red dashed box in panel A. The blue traces on the right represent changes in fluorescence intensities of GCaMP6f of the representative binned pixels (see Materials and methods). (D) Interbeat intervals (IBIs) measured from OCT and calcium imaging. Each marker represents one time interval. Each color represents one hHO. Paired t-test was used to evaluate statistical significance. N = 2 batches, n = 6 hHOs.