 Let's talk about the stroke volume. The stroke volume is the total volume of blood pumped by one ventricle in one cardiac cycle. So if you calculated the total, not all the blood pumped by the heart, but just one ventricle in the one cycle, that's going to be your stroke volume. And we have two numbers that we've already kind of identified that are going to help us calculate that. One of them was the end diastolic volume. Do you remember that? At the end, the volume that was found in the ventricle at the end of diastole, we're totally relaxed. We haven't started contracting yet and there's a certain amount of blood that's in there. We've filled passively up to 80%. We've squeezed another 24%, 20% in with the atria contracting and what we have in there at that moment is the end diastolic volume. That's the most that you can have. It's the volume at the end of diastole. And then we also evaluated end systolic volume. This was the volume that was there at the end of systole. At the end of the full contraction, there is some volume of blood left. And at that point, if we subtract those from each other, then we're going to end up with the stroke volume. The stroke volume is the amount of blood that you can push through. Stroke volume changes. Stroke volume can change based on nervous input. So if the sympathetic nervous system says, what we better get to crack in and get more blood pumping through our skeletal muscles, for example, so we can run away from the bear. I hope you know that I really do like bears. I just know that I would have a sympathetic nervous response if I saw one as if it wasn't a teddy bear. Your body can respond. I need a bigger stroke volume so that I have more perfusion through my organs so that I can get away from that bear. As opposed to who cares? Like, let's just relax, life is good. We can actually decrease the stroke volume because we just don't need that kind of perfusion. This is one of the reasons why heart rate decreases so much if you're just chilling because you don't need to be pumping as much blood. As your heart rate decreases, your stroke volume often will decrease as well. Okay, so now we're going to take cardiac, I mean, we're going to take stroke volume and we're going to see how stroke volume and heart rate interact with each other in a concept called cardiac output.