How does increased preload affect cardiac output?

Increased preload refers to the initial stretching of the cardiac muscle fibers prior to contraction, which is mainly determined by the volume of blood returning to the heart (venous return). According to the Frank-Starling law of the heart, an increase in preload results in a greater stretch of the myocardial fibers, leading to a more forceful contraction during systole. This enhanced force of contraction can subsequently increase stroke volume, which directly contributes to an increase in cardiac output.

Cardiac output is defined as the volume of blood the heart pumps per minute and is a product of stroke volume and heart rate. Thus, when preload rises, stroke volume tends to increase, leading to an overall increase in cardiac output, assuming heart rate remains constant.

In summary, when preload increases, it optimally enhances the heart's ability to pump more blood with each beat, resulting in an increased cardiac output.