CAT and hydrops fetalis: Since oxidative stress results from an imbalance between pro-oxidant activities and antioxidant defenses that buffer the ROS, we evaluated the activity of two key antioxidant enzymes in cardiomyocytes: superoxide dismutase (SOD), which converts O2− to H2O2, and catalase, which converts H2O2 to H2O. Both SOD and catalase activities were reduced in HF rats compared to Sham.