 You can think about the concept of preload as basically the amount of stretching experienced by ventricles during ventricular filling. So as the ventricles fill with blood, they stretch and the amount of stretch that they experience, that is the preload. The bigger the preload, the greater the strength of contraction. Thank you, Erno and Otto for helping us understand that. Preload, preload I like. Preload I can visualize. I can imagine that I'm loading up the heart before the contraction. Preloading, that's the pre-before amount that I'm loading into the heart. That works for my brain. Afterload is a little weirder. Afterload is related to resistance. Afterload is the resistance that says during contraction, or yeah, during contraction. It says nice try, you're not coming this way. Afterload is the resistance that, it's the force that resists blood flow. Resistence to blood flow during or after ventricular contraction, systole. So, okay, now think about that. It's not just any resistance, it's like the resistance that has to be overcome before blood will even move. So it's actually a specific quantity and you can think as dude, I want to push the blood out like going through a door. Oh, like double doors. Like if you're going to go through a double door, you have to push through the door. You have to apply a force and that's the afterload, the amount of force that you have to apply to actually get out. Once you get out, then you're out. Then you're good and there's going to be resistance out there, but that's fine. It's the initial resistance that you have to overcome to even get out of the heart at all. Afterload is greater if the blood vessels are not elastic and that's something that happens when you get heart disease, when you get cardiovascular disease. Arteriosclerosis is the hardening of the arteries and they become less elastic. They can't adjust to the changes in pressure. If you can't adjust, if you can't stretch, then you've created this like the blood, the fluid has to flow through a set diameter no matter what and that's going to be a harder task to push all that blood through there without being able to stretch and accommodate to that. Preload gets us ready to go. Afterload is what we have to overcome in order to get out. These concepts are clinically significant and we're going to mess with them in the lab for today's activity. Okay, let's look at some other things more systemically that are going to affect resistance.