Movie 4.

Serial block face scanning z-stacks through a control zebrafish heart at 5 dpf. Serial stacks through a ventricle from a myl7:Gal4;eGFP:UAS:RFP control embryo at 5 dpf. Images were obtained by serial block face scanning electron microscopy. Note the compact organization of the myocardium and the close connection between the myocardium and the endocardium, and how the sarcomeres form a continuous structure between adjacent cardiomyocytes. Of remark is also the dense border between the myocardium and epicardium. EpC, epicardial cell, EnC, endothelial cell, Ery, erythrocyte, CM, cardiomyocyte nuclei. Scale bar 10 μm.