What is preload in the context of cardiac function?

Preload is best defined as the volume of blood in the ventricles before contraction. This concept is fundamental to understanding cardiac function, particularly how the heart manages the load it needs to pump with each heartbeat. Preload is largely determined by the venous return of blood to the heart and the filling of the ventricles during diastole (the relaxation phase of the cardiac cycle).

When the ventricles fill with an increased volume of blood, the heart stretches more, which can lead to a stronger contraction due to the Frank-Starling mechanism. This mechanism asserts that an increase in the end-diastolic volume (preload) will enhance the efficiency and strength of the subsequent heart contraction.

In this context, recognizing the significance of preload helps in assessing various cardiac conditions. For example, in cases of heart failure, preload can be altered, thereby affecting cardiac output and on the overall hemodynamic state of a patient.