Allopurinol has been suggested to provide cardiovascular benefits as a result of three key actions: (1) reducing serum concentrations of uric acid which has pro-inflammatory effects [2, 5, 6]; (2) inhibiting xanthine oxidase mediated generation of reactive oxygen species which promote endothelial dysfunction and atherosclerosis plaque instability [2, 3, 7–12]; and (3) inhibiting purine catabolism thereby increasing local tissue availability of adenosine triphosphate and oxygen [8, 13, 14]. Here, XDH is linked to endothelial dysfunction.