Location:
The left coronary artery (left main coronary artery) emerges from the aorta through the ostia of the left aortic cusp, within the sinus of Valsalva. The plane of the semilunar valve is tilted so that the ostium of the left coronary artery is superior and posterior to the right coronary ostium. The left coronary artery travels from the aorta, and passes between the pulmonary trunk and the left atrial appendage. Under the appendage, the artery divides (and is thus a very short vessel) into the anterior interventricular (left anterior descending artery) and the left circumflex artery. This bifurcation can often be seen when looking into the left coronary artery ostia with a videoscope. Note that the left coronary artery may be completely absent, i.e., the anterior interventricular and circumflex arteries arise independently from the left aortic sinus.

Function:
The coronary arteries supply blood to the myocardium (heart tissue) itself; that is, coronary capillaries deliver oxygenated blood (nutrients) to all of the heart's cells. The left coronary artery and its branches supply the majority of oxygenated blood to ventricular myocardium, and additionally to the left atrium, left atrial appendage, pulmonary artery, and aortic root.

Importance in cardiovascular diseases:
Coronary artery disease is generally defined as the gradual narrowing of the lumen of the coronary arteries due to atherosclerosis. Atherosclerosis is a condition that involves thickening of the arterial walls via cholesterol and fat deposits that build up along the endoluminal surface of the arteries. With severe disease, these plaques may become calcified, increase in size, and eventually cause significant stenosis; a stenotic vessel has an increased vascular resistance relative to that of healthy vessels. A steady decrease in arterial cross-sectional area can eventually lead to complete blockage of the artery. As a result, oxygen and nutrient supply to the myocardium decreases below the level of demand. As the disease progresses, the myocardium downstream from the occluded artery becomes ischemic. Myocardial ischemia not only impairs the electrical and mechanical function of the heart, but also commonly results in intense, debilitating chest pain known as "angina pectoris." Eventually, myocardial infarction may occur if the coronary artery disease is not detected and treated in a timely manner, leading to heart failure and/or sudden cardiac death.