EMS.explained on Instagram: "Preload is specifically the degree of myocardial fiber stretch at end-diastole, right before contraction begins. This is why the Frank-Starling mechanism works: longer fibers contract harder, up to a point. When you give fluids, you’re not directly increasing preload. You’re increasing venous return, which increases ventricular filling, which then stretches the fibers. In heart failure, the ventricle overstretches past optimal length and contractility actually drops.