library_construction_protocol: Droplet based extraction: HiPSC-derived cardiomyocyte or mouse embryonic heart derived single cells were dissociated and captured and lysed using 10X Genomics Chromium Next GEM Single Cell 3' v3.1 Kit. mRNA was reverse transcribed to cDNA, and cDNA pre-amplification was conducted following manufacturer's protocol.    Smart-seq2 based extraction: HiPSC-derived cardiomyocytes were dissociated into single cell suspensions and captured using the ICELL8 Smartseq2 TAKARA system. mRNA was reverse transcribed to cDNA and cDNA pre-amplification was conducted per manufacturer's protocol on an ICELL8 nanowell chip. Droplet based library construction: Libraries for samples processed using 10X Genomics Single Cell 3' v3.1 kit were prepared from pre-amplified cDNA according to manufactrer's protocol. Gene expression libraries were generated for all 10X samples, and CellPlex multiplexing libraries were generated for running hiPSC-CM samples (Day 7, 11, 13,15, 30). Individual library index primers were used for multiplexing libraries on flow cell during sequencing.     Smart-seq2 library construction: Following Takara Smartseq2 ICELL8 protocol, pre-amplified and tagmented cDNA from individual single cells in ICELL8 nanowells received individual index sequencing barcodes for demultiplexing cells during downstream analysis.