The volume of blood in the ventricle at the end of diastole.
involves the inertia forces of inflowing blood into the left atrium during diastole which stretch its fibers, thus storing mechanical energy in them; more stretched fibers (increased preload) contract during systole with a higher force (a mechanically produced an increase in contractility known as the Frank-Starling Law)
The pressure inside the left ventricle at the end of diastole; determined by venous return and myocardial contractility and relaxation.
Force applied to resting muscle to stretch it to initial length. In heart, preload corresponds to end-diastolic filling pressure. See afterload, Starling's law of the heart.
In cardiac physiology, preload is the volume of blood present in a ventricle of the heart, after passive filling and atrial contraction. If the chamber is not mentioned, it is usually assumed to be the left ventricle.