 So the heart sounds happen, I have always thought, because the valves themselves snap shut, and what you hear is the snapping of the valves. This is not true. What you're actually hearing is the turbulence in the blood as a result of the valves closing. So I don't think there's a problem functionally or practically with thinking about the valves making noise when they close. I always envisioned it being the snapping of the actual valve pieces together, but it's the turbulence of the blood that you're actually hearing with your two heart sounds. So it makes sense that if you are having ventricular systole, the ventricles are contracting, and they are creating a high pressure zone inside those ventricles, it makes sense that the shape of the AV valves is going to prevent backflow, that the blood is going to want to go back through, not going to happen, and that's going to create, when we close it off, that's going to create some turbulence in that blood, a little bit is going to get through backwards, but then it's going to snap off, like, no, sorry for your luck, and so what was going to try to get through there, there's going to be some turbulence that you can hear with the first heart sound, which is lube. And then systole is associated with the lube. The dub is associated with the semi-lunar valves contracting, and those guys are not contracting, closing. Those guys are going to close when ventricular systole happens. The blood, you push all the blood out in systole of the ventricles, squish it all out there, there it goes, and now you relax the ventricles, the blood wants to come backwards, those semi-lunar valves are going to say, sorry for your luck, dog, they are going to close, it's going to create turbulence, that's what you're going to hear is that second sound, which is a dub. All right, so that's the mechanics of how you get the heart sounds. Go back and revisit this bad boy. Think through all the stages and make sure you're super comfortable being able to analyze, like, when you're going to hear these different heart sounds. It's showing a third heart sound that you don't have to be concerned about. All we care about are the lube and dub. Let's measure some stuff that is possible to measure thanks to our friendly Wigger diagram.