The right and left coronary arteries are the first branches of the ascending aorta, just beyond the aortic semilunar valve (Fig. 12–4). The two arteries branch into smaller arteries and arterioles, then to capillaries. The coronary capillaries merge to form coronary veins, which empty blood into a large coronary sinus that returns blood to the right atrium.
Figure 12–4. (A) Coronary vessels in anterior view. The pulmonary artery has been cut to show the left coronary artery emerging from the ascending aorta. (B) Coronary vessels in posterior view. The coronary sinus empties blood into the right atrium. QUESTION: What is the function of the coronary vessels?
The purpose of the coronary vessels is to supply blood to the myocardium itself, because oxygen is essential for normal myocardial contraction. If a coro-nary artery becomes obstructed, by a blood clot for example, part of the myocardium becomes ischemic, that is, deprived of its blood supply. Prolonged ischemia will create an infarct, an area of necrotic (dead) tissue. This is a myocardial infarction, com-monly called a heart attack.