Uric acid (urate), an organic compound comprised of carbon, nitrogen, oxygen and hydrogen, is the final oxidation product of purine catabolism in humans, higher primates and in a particular species of dog (Dalmatians). For decades it has been hypothesized that the antioxidant properties of uric acid might be protective against aging, oxidative stress, and oxidative cell injury. However, recent epidemiological and clinical evidences suggest that hyperuricaemia might be a risk factor for cardiovascular disease, where enhanced oxidative stress plays an important pathophysiological role. It has also been hypothesized that hyperuricaemia might be involved in chronic heart failure and metabolic syndrome. The apparent paradox between protective and toxic effects is supported by clinical evidences that antioxidant compounds may become pro-oxidant compounds in certain situations, particularly when they are present in blood at supranormal levels. The aim of this article is to review uric acid metabolism and physiology, highlighting its association with cardiovascular disease.