An estimated 20 patients with DCM will be randomized in a 1:1 ratio fashion to receive allopurinol or placebo. The primary aim of this investigation is to determine whether an acute infusion of intravenous allopurinol improves the inotropic response to dobutamine in patients with idiopathic DCM as measured by CMR. Specifically, the study will test the hypothesis that a single dose of intravenous allopurinol, compared to placebo, enhances delta E1 and delta E2. Secondary aims of this study are as follows: 1) to determine whether the response to allopurinol is associated with baseline XO activity and levels of natriuretic peptides (investigators predict that augmentation in delta E1 and delta E2 will correlate positively with baseline plasma uric acid and plasma B-type natriuretic peptide [BNP]); and 2) to demonstrate that tagged dobutamine CMR is a useful non-invasive technique to assess pharmacologic responses in patients with heart failure.