(a) Describe how heart contraction and relaxation influence coronary blood flow. (b) Name the major branches of the coronary arteries and note the heart regions served by each. (a) The coronary arteries are actively delivering blood to the myocardium when the heart is relaxed. The coronary vessels are compressed and ineffective in blood delivery when the ventricles are contracting. (b) The major branches of the coronary arteries and the areas they serve are as follows: The left coronary artery runs toward the left side of the heart and divides into the anterior interventricular artery and the circumflex artery.