Editing Heart (section)

===Coronary circulation===
[[File:Coronary arteries.svg|thumb|Arterial supply to the heart (red), with other areas labelled (blue).]]
{{main|Coronary circulation}}
Heart tissue, like all cells in the body, needs to be supplied with [[oxygen]], [[nutrient]]s and a way of removing [[metabolic waste]]s. This is achieved by the coronary circulation, which includes [[artery|arteries]], [[vein]]s, and [[lymph vessel|lymphatic vessels]]. Blood flow through the coronary vessels occurs in peaks and troughs relating to the heart muscle's relaxation or contraction.<ref name="CNX2014"/>

Heart tissue receives blood from two arteries which arise just above the aortic valve. These are the [[left main coronary artery]] and the [[right coronary artery]]. The left main coronary artery splits shortly after leaving the aorta into two vessels, the [[left anterior descending]] and the [[left circumflex artery]]. The left anterior descending artery supplies heart tissue and the front, outer side, and septum of the left ventricle. It does this by branching into smaller arteries—diagonal and septal branches. The left circumflex supplies the back and underneath of the left ventricle. The right coronary artery supplies the right atrium, right ventricle, and lower posterior sections of the left ventricle. The right coronary artery also supplies blood to the atrioventricular node (in about 90% of people) and the sinoatrial node (in about 60% of people). The right coronary artery runs in a groove at the back of the heart and the left anterior descending artery runs in a groove at the front. There is significant variation between people in the anatomy of the arteries that supply the heart.{{sfn|Davidson's|2010|p=525}} The arteries divide at their furthest reaches into smaller branches that join at the edges of each arterial distribution.<ref name="CNX2014"/>

The [[coronary sinus]] is a large vein that drains into the right atrium, and receives most of the venous drainage of the heart. It receives blood from the [[great cardiac vein]] (receiving the left atrium and both ventricles), the [[posterior cardiac vein]] (draining the back of the left ventricle), the [[middle cardiac vein]] (draining the bottom of the left and right ventricles), and [[small cardiac vein]]s.{{sfn|Gray's Anatomy|2008|p=981}} The [[anterior cardiac veins]] drain the front of the right ventricle and drain directly into the right atrium.<ref name="CNX2014"/>

Small lymphatic networks called [[plexus]]es exist beneath each of the three layers of the heart. These networks collect into a main left and a main right trunk, which travel up the groove between the ventricles that exists on the heart's surface, receiving smaller vessels as they travel up. These vessels then travel into the atrioventricular groove, and receive a third vessel which drains the section of the left ventricle sitting on the diaphragm. The left vessel joins with this third vessel, and travels along the pulmonary artery and left atrium, ending in the [[inferior tracheobronchial node]]. The right vessel travels along the right atrium and the part of the right ventricle sitting on the diaphragm. It usually then travels in front of the ascending aorta and then ends in a brachiocephalic node.{{sfn|Gray's Anatomy|2008|p=982}}