RCIS Practice Test 2025 – All-in-One Exam Prep

Preload refers to the amount of blood in the ventricles at the end of diastole, prior to contraction. It represents the stretch of the ventricular walls and is primarily determined by the venous return and the volume of blood filling the heart chambers during diastole. Increased filling volumes directly increase the preload, as more blood leads to greater expansion of the ventricles. This allows for a more forceful contraction according to the Frank-Starling mechanism, which states that the force of contraction of the heart muscle increases with the amount of stretch or volume of blood within the heart.

In contrast, factors such as heart rate, contractility, and filling volumes can influence preload, but none do so as significantly as the actual volume of blood that returns to the heart. Increased filling volumes ensure that there is adequate pressure and volume for optimal cardiac output. This connection is crucial for understanding cardiac function and the impact of various physiological and pathological states on the heart's performance.