Heart tissue from wide type mice were minced with a razor blade and transferred into a 15 ml conical tube containing DMEM with Collagenase I (450 U/ml), DNAse I (60 U/ml), and Hyaluronidase (60 U/ml) and incubated at 37°C for 1 hour with agitation. Digestion was then stopped by addition of HBB buffer (2% FBS, 0.2% BSA in HBSS) and filtered through a 40 μm filter into 50 mL conical, transferred to a clean 15ml conical and centrifuged at 350 x G for 5 minutes at 4°C. Supernatant was then removed and pellet resuspended in 1 mL ACK lysing buffer (Gibco, A10492) and incubated at room temperature for 5 minutes followed by the addition of 9 mL DMEM. Suspension was then centrifuged at above conditions, followed by removal of supernatant, and resuspension in 5 mL FACS buffer (2% FBS, 2mM EDTA in calcium/magnesium free PBS). Centrifugation was repeated at above conditions, supernatant removed, and pellet resuspended in 300uL cell resuspension buffer (0.04% BSA in 1X PBS) and 1uL each of CD45 (Thermo Scientific, 46162251) and DAPI (BD Biosciences, 564907) and allowed to incubate 5 minutes before sorting CD45+/DAPI- cells were collected in cell resuspension buffer. Collected cells were then recentrifuged according to above parameters and resuspended in cell resuspension buffer to a target concentration of 1000 cells/μL. Cells were counted on a hemocytometer and concentration adjusted as necessary. 10X Genomics Chromium Single Cell 5' Reagent V1.1