I am currently looking for a cardiac cell line to transfect some mutations into. As I will be doing double transfections etc. I am trying to avoid using primary cardiomyocytes, as these are hard to transfect. Also, it needs to be a cardiac muscle cells as I need sarcomeres expressing cardiac sarcomeric proteins. I found some articles on HL-1 cells obtained from mouse and they really look like a good cell line. Has anyone worked with these cells? Do they remain stable through passages, or do they tend to become genetically variable?