Zoomed view of a 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. Shown is a magnification of the myocardium in a region where sarcomeres can be observed. Note the clearly marked z-lines and the longitudinal continuity of the 163 sarcomeres between adjacent cardiomyocytes. Scale bar, 500 nm.