The coronary arteries are on the surface of the heart and are the blood vessels that supply blood to the heart muscle. The coronary arteries are generally divided into the right coronary artery and the main left coronary artery. The main left coronary artery travels downward and can be divided into two important branches, the left anterior descending branch and the left circumflex branch, and each of these branches can be further divided into a number of smaller branches. These small vessels are distributed over the surface of the heart and in turn into the muscle, thus ensuring a localized blood supply. These two branches mainly provide blood supply to the lateral and anterior walls of the heart muscle. The right coronary artery generally supplies blood to the right ventricle, but it can also provide blood supply to the lower wall and even to the apex of the heart. These coronary vessels seem to be distributed like a spider’s web across the surface of the heart to supply blood to the heart. Once a blood vessel is narrowed or blocked, angina pectoris or even myocardial infarction may occur.