Coronary collateral circulation provides an important response to ischemic heart disease and partially determines the severity of ischemic myocardial damage. Practical significance of coronary collateral circulation has long been a matter of uncertainty due to concerns about the means for gauging coronary collateral circulation and the modest populations to be representative for all patients with ischemic heart disease. It is possible that prognosis may be defined by the balance between the harm of atherosclerotic burden, and the benefit from coronary collateral circulation. Atherosclerosis acts as a potent trigger for the formation of coronary collateral circulation, but at the same time it has deleterious effects on cardiovascular morbidity and mortality. Coronary collateral circulation has a complex role in modifying the risk of cardiovascular morbidity and mortality in ischemic heart disease. A more comprehensive insight into the exact determinants of coronary collateral circulation would help establish its potential implications in clinical and epidemiological realm.