Osmosis video - Cardiac preload

Cardiac preload is the extent to which the left ventricular wall stretches at the end of diastole, or before systole starts. The amount of left ventricular wall stress is directly proportional to the ventricular end-diastolic pressure and the radius of the left ventricle, and indirectly proportional to two times the thickness of the left ventricular wall. Factors that increase preload include an increase in venous return (due to increased venous pressure or increased heart rate), an increase in arterial elastance, or an increase in myocardial contractility. Factors that affect preload include venous return, atrial contraction, heart rate, resistance from valves, and ventricular compliance.