BACKGROUND Coronary collaterals are an alternative source of blood supply to myocardium jeopardized by ischaemia. Well-developed coronary collateral arteries in patients with coronary artery disease (CAD) mitigate myocardial infarcts and improve survival. METHODS AND RESULTS Collateral arteries preventing myocardial ischaemia during brief vascular occlusion are present in 1/3 of patients with...