It is well established that endothelial dysfunction is an early marker of cardiovascular disease and associated with poor outcome in coronary artery disease. Endothelial dysfunction is triggered by common cardiovascular risk factors such as type 2 diabetes and dyslipidemia. The molecular mechanisms underlying development of endothelial dysfunction include reduced bioavailability of nitric oxide (NO) and formation of reactive oxygen species (ROS) regulated by arginase. Arginase is upregulated in cardiovascular disease and diabetes, which contributes to cardiovascular dysfunction via reduced bioavailability of NO and increased oxidative stress. Recent data indicate that similar signaling events occur in the red blood cell (RBC). The RBC plays a role in the regulation of cardiovascular function via a mechanism involving RBC arginase and endothelial NO synthase. RBCs are able to export cardioprotective NO bioactivity under tight regulation of arginase. Inhibition of RBC arginase protects the myocardium from ischemia-reperfusion injury via a mechanism strictly dependent on endothelial NO synthase. Arginase is upregulated in patients with type 2 diabetes. This change promotes increase in RBC ROS production via NO synthase uncoupling, increased myocardial ischemia-reperfusion injury and development of endothelial dysfunction. Inhibition of arginase and ROS formation in RBCs from patients with type 2 diabetes prevents the development of endothelial dysfunction and improves cardiac tolerance to ischemia. These data point towards a novel regulatory role of the RBC in cardiovascular disease, and targeting RBC dysfunction may be a beneficial therapeutic strategy.