 Before we go on to understand the Cordillary Arterial Anatomy, let's quickly look at the Cadet Chambers on Axial CT, I'll be scrolling craniocaudally. On this first image, we have the ascending ovata on the right side, main pulmonary trunk on the left side. This is the left auricle and the posterior most chamber here is the left atrium. We have the pulmonary veins opening into the left atrium. As I scroll down, we have the aortic root here. This is the left coronary sinus. It is giving off the left main coronary artery. This is the right ventricular outflow tract. This triangular shaped structure on the right side anteriorly is the right auricle. The left atrium with the pulmonary veins. Further down, we have the right ventricle. We have the left atrium, the right auricle, the right atrium, the aortic root still with the right aortic sinus giving off the right coronary artery and the non-coronary sinus on the right side posteriorly. As I scroll further down, we have the left ventricular outflow tract. This is the left ventricle. This is the right ventricle, the right atrium and the left atrium. Further down, this is kind of a four chamber view wherein we have the right ventricle which is anterior and to the right left ventricle which is to the left and posterior the left atrium. This is the mitral valve between the left atrium and the left ventricle. This is the right atrium with the tricuspid valve between the right atrium and the right ventricle. Before we go on to understand the course of the coronary arteries, these are the few terminologies we need to know. Between the right ventricle and the left ventricle, we have a groove which is called the interventricular groove. In the cranial aspect of the heart, it is the anterior interventricular groove and as we scroll down and reach the base of the heart, it becomes the posterior interventricular groove. Between the left ventricle and the left atrium, what runs is the left atrio ventricular groove. So, posteriorly and to the left is the left atrio ventricular groove. Exactly diagonally opposite to it, we have the right atrio ventricular groove which runs between the right ventricle and the right atrium. This is the inferior portion of the right atrio ventricular groove. The point where this atrio ventricular groove meets the posterior interventricular groove is termed as the crux of the heart. The point exactly diagonally opposite to it is the apex of the heart. In this case, the apex of the heart is pointing towards the left side. Now let's go back cranial. We have the left coronary sinus. Left coronary sinus gives of the left main coronary artery. This is the left main coronary artery which runs between the RVOT, right ventricular outflow tract and the left atrium. It divides into two branches. The branch which courses anteriorly is the left anterior descending branch and the one which courses posteriorly is the left circumflix branch. Left anterior descending artery then gives off two branches. One is the diagonal and the other is the septal. The diagonal branch on the left side of the left anterior descending artery and courses towards the free wall of the left ventricle. So we have a diagonal branch of the left anterior descending artery here and the septal branch always courses towards the septum. So in this case, we have the septal branch. This is a very small septal branch which is coursing towards the interventricular septum. So whatever arises from the LAD and courses towards the left side is the diagonal and the one which courses towards the septum is the septal. Left anterior descending artery runs in the anterior interventricular groove. So whatever runs in the anterior interventricular groove to reach the apex of the heart is called the left anterior descending artery. In this case, the diagonal branch is quite good sized. That is also giving off another small branch here. Now the posterior branch of the left main coronary artery is the circumflix branch. So we have a small circumflix branch here. The circumflix artery courses in the left itrioventricular groove. So it courses in the left itrioventricular groove and it gives off what we call the obtuse marginal branches. If you can see here there is a small branch coming off the proximal circumflix which is the small obtuse marginal or popularly known as OM branch. As I scroll down the circumflix artery running in the left AV groove gives off another branch. This is OM2 branch and then it continues further as OM3 branch. So we have the OM3 branch. These branches supply the lateral wall of the left ventricle. Now going back to the aortic sinuses, we have the right aortic sinus which gives off the right coronary artery. Right coronary artery in this case is very good sized. It is a dominant artery. The right coronary artery gives off the first branch which is seen coursing posteriorly and it is coursing towards the left atrium. So this is a SA nodal branch. In almost 60% of the patients of the population it arises from the right coronary artery. In the rest 40% it may arise from the left circumflix branch. So this is the SA nodal branch. Before we go further on to the right coronary artery we can see a tiny branch here which is arising directly from the right coronary sinus and it is curving around the right ventricular outflow tract. This is a conal branch. Now in almost 60 to 70% of the population the conal branch arises from the right coronary artery. However in around 20 to 30% it may arise directly from the right coronary sinus. Another small branch here this is a right ventricular branch of the right coronary artery. As I scroll down further there is another branch which is coming off the right coronary artery. It is coursing along the acute margin of the heart and hence it is called the acute marginal artery. So we have the acute marginal branch of the right coronary artery and as the right coronary artery courses down into the posterior atrioventricular groove at the crux of the heart it branches into this artery which is seen coursing in the posterior interventricular groove that is the posterior descending artery and another large branch which is running across in the left AV groove and also supplying the lateral wall of the left ventricular. This is the posterior lateral ventricular branch. In this case the right coronary artery is giving off the PDA and the PLV branches and hence is the dominant artery. There are times when the circumflex artery is dominant. When do we call it dominant? The circumflex artery when it courses in the left AV groove towards the crux of the heart and divides into PDA and PLV branches that is when we call it a dominant artery. In 30% of the population the circulation is co-dominant that is the right coronary artery gives off the posterior descending branch and the left coronary artery gives off the PLV that is the posterior lateral ventricular branch.