Coronary collaterals are anastomotic connections without an intervening capillary bed between portions of the same coronary artery and between different coronary arteries. The main determinants of coronary collateral circulation are preinfarction angina, severity of coronary artery disease, significant pressure gradient and an increase in shear stress. In presence of pressure gradient the blood flow is redistributed through the preexistent arterioles that connect a high-pressure with a low-pressure area. The consequence is an increased flow velocity and therefore increased shear stress in the collateral arteries, which leads to a marked activation of the endothelium with the subsequent morphological changes, vascular remodeling and activation of growth factors involved in angiogenesis and arteriogenesis. Well-developed coronary collateral circulation can be observed in 25% to 37% of patients with one vessel coronary artery disease and in 74.7% patients with extensive disease. Recruitable collaterals can be evaluated by performing coronary angiography, a qualitative or semiquantitative technique and by measurement of pressure and velocity in distal vascular beds (quantitative technique). Demonstration of well-developed collaterals in patients with angina pectoris or myocardial infarction has been associated with limited infarct size, improved ventricular function, less ventricular aneurysm formation and improved in-hospital and long-term survival.