I have been trying to culture primary cardiomyocytes from neonatal Rat heart using PIERCE Cardiomyocyte isolation kit. I have plated the cells 4 days back and changed the medium after 48 hours. But still, the cells attached are very low in number. Also, smooth muscle cells and fibroblasts are dying off. I am pretty sure, cells are not contaminated as the medium color isn't yellow. I would appreciate any sort of suggestions regarding this. Thanks.