In the present study,effects of hypoxia on cardiomyocyte apoptosis and activity of antioxidant enzymes in the Megalobrama amblycephala heart were studied.The results showed that hypoxia caused changes of heart structure and mitochondrial damage by using HE staining and electron microscope observation.Moreover,hypoxia induced cardiomyocyte apoptosis and the Bcl-2 mRNA expression changes by using TUNEL and quantitative real-time PCR methods.In addition,the results revealed that moderate hypoxia could result in the decrease of the MDA content and SOD activity of the heart mitochondria extracted by sucrose gradient centrifugation.