 EXTRACARDIAC-TO-CORONARY COLLATERAL SUPPLY Commonly, coronary collaterals are implicitly understood to exist between coronary artery branches. However, the structural existence of coronary collaterals with an extracardiac connection has been confirmed by anatomical investigations. Pathophysiologically and with regard to a potential for arteriogenic stimulation, the connections from the internal mammary arteries, are of special interest. Indeed, before the advent of coronary bypass surgery, several clinical studies examined the usefulness of a minimally invasive surgery to augment collateral flow to the heart via these internal-mammary-to-coronary-artery connections in patients with angina pectoris. The performed distal bilateral ligation of the internal mammary arteries was thought to improve flow over naturally pre-existing anastomoses between the internal mammary arteries and the coronary circulation. 