 Now let's talk about the venous drainage of the heart. The most important venous drainage of the heart is the coronary sinus. So let's start off with how the coronary sinus is formed. The coronary sinus is formed by a vein which runs up like this in the intraventricular groove anteriorly. And it is not visible here because it has been removed during the dissection, but it accompanies the LAD largely. And that is known as the anterior intraventricular vein. As it climbs up in accompaniment with the LAD, it reaches the left part of the coronary groove. And there it becomes known as the great cardiac vein. And we can see the beginning of the great cardiac vein here. I've lifted it up. So in the coronary groove, the great cardiac vein accompanies the circumflex artery. Now here we have an anatomical curiosity. In the left part of the coronary groove, the circumflex artery and the great cardiac vein, they both run together. And this is one of the places in the human body where an artery and a vein are both carrying blood running in the same direction, which is contrary to the anatomical rule. In this region, it receives a vein and we can see that vein here. This is the left marginal vein. And this left marginal vein opens into the great cardiac vein. The great cardiac vein then continues. And now it is running in the posterior part of the coronary groove. And here it meets with this vein coming from the left atrium, this vein. This is known as the oblique vein of the left atrium, which opens here. Once the oblique vein of the left atrium opens into the great cardiac vein, then now it becomes known as the coronary sinus. And we can see the full length of the coronary sinus here, running in the posterior part of the coronary groove. And finally, the coronary sinus then opens into the right atrium. And I will show the opening of the coronary sinus in the right atrium just now. Now we are showing the interior of the right atrium. And you can see the probe has gone into an opening. And that opening is the opening of the coronary sinus in the right atrium. And if we trace the other end of the probe, we can feel it inside the coronary sinus. So this is the opening of the coronary sinus in the right atrium. The opening of the coronary sinus is close to the interatrial septum. And it is also close to the region of the atrioventricular node, AB node. I would like to draw your attention to these filamentous structures near the opening. This is the remnant of the valve of the coronary sinus, which is present. And it is also known as the thebesian valve. So this is the termination of the coronary sinus. Now let's take a look at the tributaries of the great cardiac vein and the coronary sinus. And for that, I'm going to bring the heart around so that we can see the posterior aspect again. So we are seeing the great cardiac vein and the coronary sinus in the posterior coronary groove. Let's take a look from the left to the right. We have the following. First we have this tributary. This is the left marginal vein. This left marginal vein accompanies the left marginal artery or the obtuse marginal artery, which is the branch of the circumflex artery. The second tributary is this one here. This is the left posterior ventricular vein, which is on the posterior surface of the left ventricle. The third tributary is this one here. This is the major tributary. This is the middle cardiac vein. The middle cardiac vein runs in the posterior intraventricular groove along with the posterior descending artery. And this also opens into the coronary sinus. And the final tributary is this one here. This is the small cardiac vein. The small cardiac vein runs on the right margin of the heart along with the right marginal artery. And this opens into the coronary sinus close to its termination in the right atrium. So going from left to right, we have the left marginal vein, posterior ventricular vein, middle cardiac vein, small cardiac vein. So these are the four tributaries which open into the coronary sinus. And before I conclude, I have to show yet one more, which is not very commonly seen, but we can see it in our dissection here. We can see a vein opening directly into the right atrium here, this vein. This is an anterior vein of the right atrium. And we can see this, it is opening directly into the right atrium. And finally, there are a few minor veins which are not visible, where they are known as the smallest cardiac veins or the venae cordis minimae, which can directly open into any of the chambers of the heart, but usually they open into the right atrium. In this connection, I can mention one latest technology which is being employed nowadays, and that is known as trans-myocardial laser recanalization, whereby means of laser, they are actually making small holes in the myocardium and allowing the blood to perfuse from the chambers of the heart into the myocardium. And that is called trans-myocardial laser recanalization. And that is a new technique of re-perfusing the myocardium, especially those areas of the myocardium which have undergone ischemia. So that is all for now about the coronary circulation. Thank you very much for watching. If you have any questions or comments, please put them in the comment section below. Dr. Sanjay Sanyal, signing out. Have a nice day.