Left Ventricular Preload
According to Kaplan, preload is technically defined as ventricular wall stress at end-diastole [Kaplan JA, ed. Essentials of Cardiac Anesthesia. Saunders, 2008 p 60], however, ventricular volume at end-diastole may be a more clinically useful definition – first, it is more easily measured (by echocardiography) and second, it is the geometrical configuration of the ventricle (in particular, interactions between actin and myosin) that determines the maximum amount of wall-stress generated.
Ventricular preload can be altered by blood volume, intrathoracic (and pericardial) pressure, body position, venous tone, exercise, atrial function, valvular stenosis, and ventricular thickness.
Normally related to contractility via the Frank-Starling curve, whether or not there is a descending portion of the Frank-Starling curve in humans is a matter of debate [Parker JO and Case RB. Circulation 60: 4, 1979].