Flashfrozen hearts were homogenized with a TissueLyser II (Qiagen), filtered through a 40 uM strainer and centrifuged at 1200g, 5 minutes, 4C. Resuspended nuclei were FACs sorted for quality and fractionated with the 10x Genomics Chomium iX according to manufacturer's protocol. The 10x Genomics Chromium Single Cell Reagent Kit (v3.1) was used to generated expression libraries. Libraries were sequenced with a NovaSeq 6000 (Illumina).