The isolation and identification of exosomes were conducted following our previous procedure (43 (link)). Briefly, the supernatant of the hiPSC-CMs was collected after cultured in exosome-free medium for 48 hours and centrifuged at 300g for 10 min. The cells, membranes, and debris were removed by a series of ultracentrifugation. After filtered through a 0.22 μm filter (Millipore), the supernatant was then ultracentrifuged at 120,000g for 90 min to obtain exosomes. Subsequently, the exosomes were resuspended in DPBS and purified at 120,000g for 90 min. Last, the exosomes were washed with DPBS and stored at −80°C until use. The protein makers of exosomes (CD9, CD81, Alix, and Syntenin) were examined by Western blotting. The microstructure of exosomes was observed under TEM (Hitachi). The diameter of particles in exosomes was measured using NTA (Zetaview). The zeta potentials of exosomes were analyzed by using a Zetasizer Nano analyzer (Malvern). To visualize the location of exosomes in cells after the uptake by primary cardiomyocytes, PKH-26 was used to label exosomes according to the manufacturer’s instructions (Sigma-Aldrich).