Bought the HL-1 cells from EMD Millipore early this month. Thawed the vial into a T-25 flask. All was going great and they were beating fine, until this one day where the cells overgrew and kind of started losing the beating/Contractility. I have not been able to get them going ever since.

Also I had frozen 4 T75 down which were beating but not as great as they should have been. When I thawed a vial of the recent frozen cells. I see a few cells beat at day 2 but that goes away on day 3.

Any pointers of what I could change or add to get these cells to work would be great.