Arginase is a ubiquitous enzyme that regulates polyamine- and nitric-oxide-requiring vascular functions. It is well-established that, in mammals, arginase overactivation contributes to endothelial dysfunction, a hallmark of cardiovascular diseases. The pharmacological potential of arginase inhibition for improving vascular function is largely supported by a wide range of data from animal studies. However, caution is required before extrapolating animal data to humans because interspecies differences in arginase expression and localization have been observed. For this reason, this review presents the existing arguments from human data in favor of a role of arginase in cardiovascular diseases. Then, the available data from clinical studies are discussed, as well as the possible arginase inhibitors that might be used in future large-scale clinical trials.