 In this video, we're gonna be discussing coronary artery anatomy. This is a really high yield concept for a USMLE step line and when you're gonna get a lot of questions on and understanding the anatomy of the coronary arteries, it's gonna help you understand a lot of other concepts within cardiology. And what exactly are the coronary arteries? Those are just the arteries that give blood supply to the heart itself. So things like the left ventricle, the right ventricle, the conduction system of the heart are all supplied by various coronary arteries, okay? Let's begin our discussion by orienting ourselves to our diagram here. This is an anterior view of the heart. That means you've got our apex over here and the base on the side. One thing you'll notice right off the bat is that the coronary arteries branch off of the aorta, okay? And they're divided into two main divisions. You've got the left main coronary artery or LCA and the right main coronary artery or the RCA. Let's start with the left side. So you see the left main coronary artery here. Again, it branches directly off of the aorta and it's divided into two parts. It bifurcates into the left anterior descending artery and the left circumflex artery, okay? And what is the left anterior descending artery supply? It supplies the interior part of the left ventricle, the interior part of the interventricular septum. And the interventricular septum is just the septum that divides the left ventricle and the right ventricle, okay? And you'll notice when you study coronary artery anatomy that a lot of blood supply is dedicated just to the left ventricle. That's because it's a really hardworking chamber of the heart and it's gonna require a lot of blood. And it's important to understand which various parts of the left ventricle are supplied by which artery. So now you can remember that the interior part of the left ventricle is supplied by the left interior descending artery, okay? And you can see a picture of the left interior descending artery here. How about the left circumflex artery? The left circumflex artery supplies the lateral part of that left ventricle. Again, a lot of blood supply dedicated just to the left ventricle. And here's where things get a little tricky. There's something called the posterior descending artery or the PDA. And in five to 10% of the population, the PDA branches off of the left circumflex artery, okay? And in the other approximately 90%, it'll branch off the right main coronary artery. And we'll discuss why that's important later in the video, but what is the PDA supply? It gets the inferior part of that left ventricle, the AV node, then the inferior part of the interventricular septum. Why is it important that the PDA supplies the AV node? That's because if you have an occlusion of the posterior descending artery, a myocardial infarction that involves the posterior descending artery, you could generate an arrhythmia because the AV node loses its blood supply. I've personally had a lot of practice questions in USMLE questions about this topic. So it's one you definitely wanna remember, okay? Let's jump to the right side now. What is the right main coronary artery supply? It gets the right ventricle and the SA node. Again, it's really important to remember that the SA node is supplied by the right main coronary artery because you can generate an arrhythmia as a result of an occlusion of the right main coronary artery. And as I mentioned before, the posterior descending artery, 90% of the population has the posterior descending artery branching off of the right main coronary artery. You can see an example of that here, the posterior descending artery branching off of the right coronary artery. Again, going back to the aorta, okay? And just reiterating that the posterior descending artery supplies the inferior part of the left ventricle, the AV node, and the inferior part of the interventricular septum. And the concept of the posterior descending artery branching off the right main coronary artery versus the left circumflex artery gives rise to a concept called heart dominance, which we'll discuss now.