Fig. 3.  Celecoxib exposure prevents heart valve formation. Experiments were performed three times. Scale bar: 20 μm. (A, B ) In vivo  confocal images of transgenic Tg(flk1:GFP)  zebrafish, in which vascular endothelial cells express green fluorescent protein (GFP), show valve and endocardial morphology with atrium (a) and ventricle (v) in 96-h postfertilization embryos treated with 0.3% dimethyl sulfoxide (DMSO) or 25 μM celecoxib. Arrowheads  point to the atrioventricular junction and an arrow  indicates the heart valve. (C ) Summary of heart valve formation in 96-h postfertilization embryos as analyzed by chi-square test. (D, E ) Successive images during heartbeat by high-speed confocal scanning with an interval of 160 ms. **P < 0.01; ***P < 0.001.