Reactive oxygen species are mainly generated in mitochondria.43, 44 They can also be produced in cytosol and membranes in response to different stimuli including growth factors and inflammatory cytokines.44 Several enzymes including NADPH oxidase participate in ROS generation.45 In this study, we showed for the first time that myocardial gene expression of the NADPH oxidase subunits NOX 2 and NOX 4 is not increased in AS rats with heart failure and is not modulated by physical exercise. The gene discussed is FMO5; the disease is aortic stenosis.