In chronic heart failure, the sustained elevation of plasma adrenaline and noradrenaline levels resulting from over-activation of the sympathetic system was associated with aggravated oxidative stress due to abnormal activation of the non-phagocytic NAD(P)H oxidase in response to noradrenaline [10] and transformation of catecholamines into “aminochromes” undergoing redox cycling in mitochondria to excessively generate ROS [8,15]. Here, FMO5 is linked to congestive heart failure.