Oxidative stress, an imbalance between the formation and degradation of free radicals within the myocardium, contributes to metabolic derangements in patients with DCM. The enzyme xanthine oxidase (XO), a potent source of oxidative stress, is expressed in the failing heart, and it uncouples cardiac energy consumption from cardiac contraction in the setting of chronic heart failure. These effects can be reversed by inhibiting XO with the XO inhibitor allopurinol, resulting in a marked increase in cardiac efficiency. These findings provide a rationale for using allopurinol to enhance cardiac function in DCM. However, there is little data on the effects of allopurinol therapy on cardiac function. Therefore, the primary aim of this study is to determine whether an acute infusion of intravenous allopurinol improves the inotropic response to beta-adrenergic stimulation in patients with idiopathic DCM.