Final answer:
Increased preload is most likely caused by an increase in venous tone, as it enhances venoconstriction and therefore increases the volume of blood returning to the heart, stretching the ventricular muscle more according to the Frank-Starling principle.
Step-by-step explanation:
An increased preload in the context of the cardiac cycle is most likely caused by an increase in venous tone, which leads to venoconstriction and enhances the return of blood to the heart. Preload, also known as end-diastolic volume (EDV), is the volume of blood in the ventricles at the end of diastole, before the heart contracts.
An increased venous tone results in increased preload because it increases the amount of blood returned to the heart, thus stretching the cardiac muscle more before contraction pursuant to the Frank-Starling principle. Options such as arteriolar tone, myocardial contractility, heart rate, and capillary permeability do not have a direct relationship to increasing preload as venous tone does.