CAT and congestive heart failure: In the same way, the study by Michałek et al. reported that serum CuZn-SOD activity and serum total antioxidant capacity were significantly lower in their study groups compared to in control animals; specifically, they found that catalase activity was significantly higher and plasma GPx activity was significantly lower in dogs with chronic heart failure and AF compared to those with chronic heart failure only, sinus rhythm, or control dogs.54