Abstract: @@ Heart failure is currently one of the most common and most cost-intensive of the chronic diseases.1 The main cause of chronic heart failure (CHF) is the abnormalities of both cardiac contractile performance and myocardial energy metabolism. Elevated levels of reactive oxygen species (ROS) have been proposed to contribute to both of them. Xanthine oxidoreductase (XO)is a major source of ROS in the cardiovascular system.