Like all body organs, the |heart| needs a supply of ~blood~ to bring it oxygen. It cannot get oxygen from the ~blood~ within its chambers, which passes through too quickly and under too great a pressure, and in the right side is very low in oxygen. Instead, the muscle that makes up the wall of the |heart|, the |myocardium|, receives oxygen-rich ~blood~ from a system of small arteries that branch from the |aorta|. These are called the coronary arteries. They cross over the |hearts| surface, dividing and sending tiny branches into the |heart| muscle. The two coronary arteries are no wider than a drinking straw. The |right coronary artery| lies in a groove between the right atrium and right ~ventricle~ and loops around the lower side and to the rear of the |heart| like a crown. Hence the name, coronary. This |artery| supplies ~blood~ to the thick muscle of the right ~ventricle~. On the other side, the |left coronary artery| divides almost immediately into two large branches, one of which (the ~anterior~ descending branch) passes over the front of the |heart| toward the tip. The other branch (the circumflex branch) lies in a groove between the left atrium and left ~ventricle~. This |artery| supplies ~blood~ to the muscle of the left ~ventricle~. The ~anterior~ descending branch supplies the front surface and tip of the |heart| and the front part of the |septum|. The circumflex branch supplies the portion of the left ventricular wall away from the |septum|. From the large coronary vessels, smaller branches arise, which divide and insert into the |heart| muscle, supplying its nutritional needs. If a ~blood~ clot occludes (blocks) some part of the |coronary artery|, as in coronary thrombosis or coronary embolism, the cells of the |heart| are deprived of oxygen and soon die. This is called ~myocardial infarction~.
