Final answer:
The x-axis represents preload and the y-axis represents stroke volume on the Frank-Starling curve.
Step-by-step explanation:
The x-axis of the Frank-Starling curve represents preload, which is the stretch on the ventricles prior to contraction. The y-axis represents stroke volume, which is the volume of blood pumped out of the heart with each contraction. Preload is determined by factors such as venous return and filling pressure of the heart, while stroke volume is influenced by factors like contractility and afterload.