 So this is the heart I'm holding in my hand and we have dissected out the epicardium and we have removed the sub-epicardial fat to show the vasculation. The most important venous drainage is this structure which I'm tracing. This is the coronary sinus. But how is the coronary sinus formed? For that let's come to the anterior surface of the heart or the sternocostal surface of the heart. So I've turned the heart back and we are seeing looking at the sternocostal surface. So this is the anterior intraventricular group. We can see a vein running in the anterior intraventricular group and that is this vein here. This accompanies the anterior descending artery, anterior intraventricular artery. This is known as the anterior intraventricular vein. So this is where the whole thing starts. This anterior intraventricular vein runs up and it reaches the left part of the coronary groove and here it makes a bend. Once it reaches the coronary groove, here it is known as the great cardiac vein. This great cardiac vein is accompanied by the circumflex artery and they run together in the left part of the anterior intraventricular groove. And here we have a very unique anatomical curiosity. Normally when an artery accompanies a vein, we know from our general knowledge of anatomy that arterial blood flows in one direction and the venous blood flows in the opposite direction. This is one of the rarest of rare places where we have an artery and a vein running together and the blood in both of them are flowing in the same direction. The circumflex artery blood is also flowing in this direction. Great cardiac vein blood is also flowing in the same direction. It runs to the posterior surface of the heart. It is still called the great cardiac vein and in the posterior part of the anterior intraventricular groove, it receives this vein here. This is a small vein which comes from the left atrium and this vein is referred to as the oblique vein of the left atrium. This oblique vein of the left atrium is an embryological remnant of the left superior vena cava. Once the oblique vein of the left atrium opens into the great cardiac vein, then it becomes known as the coronary sinus and this is the coronary sinus. It is called coronary sinus because it runs in the coronary groove. The posterior part of the coronary groove and this is the most important final venous drainage of the heart. And this then opens into the right atrium. This is the opening of the inferior vena cava and this is the opening of the superior vena cava. So I am putting my probe inside the opening of the inferior vena cava and we can see my probe has come into the coronary sinus. In this particular cadaver, there was an anatomical variation. Instead of having one opening of the inferior vena cava, there were two openings of the inferior vena cava and we can pass it through the second opening and we can still enter into the coronary sinus. At the point of its opening, there may be a valve that is known as the Thebiscian valve of the coronary sinus. But that we can see only once we open out the atrium. So this is the full course of the coronary sinus, its formation and its drainage. Now let me mention the tributaries of this coronary sinus. So for that, let's start again from the front. This was, as we had mentioned, the anterior intraventricular vein and this receives this first tributary. This is referred to as the left marginal vein and we can see it is opening into the anterior intraventricular vein. Then we have the next tributary. Again I am turning the heart. We have left posterior ventricular vein. This runs on the posterior surface of the ventricle and this opens into the coronary sinus. Then we have the next major tributary and that is this one which I have lifted up here. This is the other portion of it. This is known as the middle cardiac vein. The middle cardiac vein runs in the posterior part of the intraventricular groove in accompaniment with the posterior descending artery, which is the continuation of the RCA and this is the next major tributary of the coronary sinus. And this is the place where it was opening into the coronary sinus. And then as I turn the heart further, now we have come to the right margin of the heart, we can see this tributary here. This is the small cardiac vein. So this is the terminal portion of the small cardiac vein opening into the coronary sinus. And this is the other portion of the small cardiac vein which is opening into the coronary sinus. So this is the small cardiac vein. In this particular cadaver we noticed one bluish section of atrium here. This we have made a small incision to look into it and we noticed that this is a small area of venous hemorrhagic infarction. We can see some tributaries on the right margin of the heart which are opening into the small cardiac vein. And these tributaries accompany the right marginal artery which is the branch of the RCA. So these are the tributaries which open into the coronary sinus. Apart from that we have a few other veins and we can see that when I turn the heart back and now I'm looking again at the sternocostal surface or the anterior surface and we can see some veins opening directly into the right atrium. One of them is here, another one is here. These are known as the anterior cardiac veins. They open directly into the right atrium. Not visible here, smallest cardiac veins or the thebacian veins. They are numerous, they are bi-directional, they are valueless and they can open in any chamber of the heart but they mostly open into the right atrium. So this is the full venous drainage of the heart. Before I conclude I would like to draw your attention to an interesting observation. We notice that the vascular system inside the major vascular system on the heart are highly tortuous. We can see the anterior descending artery is tortuous. Similarly we can see that the posterior descending artery is also very tortuous. The reason for this tortuosity is that it's an anatomical fact. Wherever an artery is located in a structure or an organ which is mobile the vessel has to be tortuous to compensate for the mobility. That's all for now. Thank you very much for watching. Dr. Sajya Sanyal signing out. Please like and subscribe. If you have any questions or comments please put them in the comment section below. Have a nice day.