Preload and Afterload for Ventricles of the Heart
Preload
Is the load on muscle even before the muscle starts contracting.
For ventricular muscles, it's the amount of blood in the ventricles before they begin to contract.
Basically its End Diastolic Volume (EDV).
Afterload
Afterload is exerted on muscle after it starts contracting.
For ventricular muscles, it's the pressure in the aorta.
Resistance in circulation can also be considered as an afterload.