Step	Problem	Solution
1A(viii)	Usually 25–35% of the cells will be positive for Isl1 but occassionaly the percentage of Isl1-RFP cells is less than 10%	Incubate the EBs for 12–24 hours longer to increase the percentage of isl1+ cells
1A(xi)	High percentsge of sorted dead cells	Add DAPI to FACS sorting solution (dilution 1:2000) to stain and exclude dead cells. In addition, to improve cell survival, consider adding 10mM Rock inhibitor to the FACS sorting solution
B(ix)	Low percentage of hiPSC-CMs	Incubate the cells at day 9, in RPMI without glucose and 5 mM of sodium lactate. Change the medium every other day for a maximum of 4 days. Then continue culturing the cells in RPMI-B27 without Vitamin A.
B(x)	Low percentage of isl1+ human CPCs	optimize the cell differentiation protocol by testing different concentrations of CHIR99021 (up to 10mM depending on the hiPSC line) and XAV939. Additionally, try analyzing CPCs 12–24 hours later.
2	Increased post-procedure mortality due to prolonged hypothermia	Monitor closely the pups while they are on ice.
5	Pups develop bleeding during surgery	Use hypothermia during surgery and fine forceps with blunt ends.
8	CPCs do not engraft or the final number of cells is low,	Use a previously published prosurvival cocktail32 to increase the engraftment and survival of the transplanted cells