Which of the following statements about collaterals in the normal coronary circulation is true?

B. The coronary arterial bed has minimal effective collaterals

DISCUSSION: The collateral circulation to the heart is relatively poor. In the human heart there are few natural collaterals of sufficient diameter for delivery of a significant quantity of blood. Most of the collaterals are approximately 200 mm. or smaller, and channels of this size cannot conduct significant quantities of blood for cardiac requirements. There is no absolute example of anatomic end-arteries in humans. While the magnitude of arterial collateral circulation varies considerably, all organs have some collaterals.