The clinical variable predicting the development of collateral arteries in humans is the hemodynamic severity of coronary stenoses. Hyperemia induces an overall increase in coronary collateral flow in patients with coronary artery disease (CAD). There is a reduction in hyperemia-induced myocardial perfusion in the collateral-dependent vascular area in about 10% of patients with CAD and superior collateral vessels (collateral steal). Collateral recruitment has a major impact in the equation: ischemic tolerance=preconditioning+collateral recruitment.