The role of coronary collateral circulation in limiting ischemia and infarction has been studied prospectively. Transient occlusion of a coronary artery angioplasty has provided evidence that collateral circulation decreases wall motion abnormalities, ST segment changes, and lactate production. Patients who have collateral flow also have a better outcome after coronary artery dissection and acute closure than patients without collateral flow. Collateral circulation also limits infarct size during acute myocardial infarction with and without thrombolysis. Although collateral flow may decrease coronary artery bypass graft patency in certain subgroups of patients, the perioperative infarct rate and mortality is decreased. Growth factors have been identified that increase the development collateral circulation and may improve ventricular function in the setting of myocardial infarction.