The left coronary artery arises from the left posterior aortic sinus. It runs to the left behind the pulmonary trunk and appears between left auricle and pulmonary trunk. In that position the artery divides into anterior interventricular branch and circumflex artery. Circumflex artery turns round the left border of the heart runs through the coronary sulcus between left atrium and left ventricle on the posterior surface of the heart in the posterior part of the atrioventricular groove. It ends by anastomosing with the terminal part of the right coronary artery. The left coronary artery is larger in size than the right coronary artery. The average diameter of left coronary artery is 4 mm. The left coronary artery supplies left ventricle, left atrium, anterior two third of the IV septum and adjacent part of the right ventricle.