Metalaxyl is an anilide pesticide that is widely used to control plant diseases caused by Peronosporales species.In order to study the toxic effects,zebrafish embryos were exposed to metalaxyl at nominal concentrations of 5,50 and 500 ng/L for 72 hr,and the cardiac development and functioning of larvae were observed.The results showed that metalaxyl exposure resulted in increased rates of pericardial edema,heart hemorrhage and cardiac malformation.The distance between the sinus venosus and bulbus arteriosus,stroke volume,cardiac output and heart rate were significantly increased in larvae exposed to 50 and 500 ng/L metalaxyl compared to solvent control larvae.Significant upregulation in the transcription of tbx5,gata4 and myh6 was observed in the 50 and 500 ng/L treatments,and that of nkx2.5 and myl7 was observed in the 5,50 and 500 ng/L groups.These disturbances may be related to cardiac developmental and functional defects in the larvae.The activity of Na+/K+-ATPase and Ca2+-ATPase was significantly increased in zebrafish embryos exposed to 500 ng/L metalaxyl,and the mRNA levels of genes related to ATPase (atp2a11,atp1b2b,and atp1a3b) (in the 50 and 500 ng/L groups) and calcium channels (cacna1ab) (in the 500 ng/L group) were significantly downregulated;these changes might be associated with heart arrhythmia and functional failure.