GPX3 and atrial fibrillation: The increase in the ROS concentration and therefore of oxidative stress in AF may result from either the up-regulation of pro-oxidant enzymes, such as Nicotinamide Adenine Dinucleotide Phosphate Hydrogen (NADPH) () oxidase, or the down-regulation of antioxidant defences including glutathione peroxidase 3 (GPx3) and superoxide dismutase (SOD), which are among the most important circulating antioxidant enzymes [42].