Inhibiting heartbeat impairs expansion of the epicardium. Lateral confocal images of zebrafish hearts at 120 hpf with anterior to the left. The epicardial marker, pard3, is green and ALCAM (cardiomyocytes) is red. Arrows in panels A and C indicate epicardial cells on the ventricle (n = 7 per group). (A) Control. (B) BDM added at 48 hpf and maintained to the end of the experiments. (C) BDM added at 72hpf and maintained to the end of the experiments. For all panels, V is ventricle; A, Atrium. Scale bars = 50 microns.