Which physiological change occurs in response to an increased preload?

Increased preload refers to the initial stretching of the cardiac muscle fibers prior to contraction, which is directly related to the volume of blood filling the ventricles during diastole. When preload is increased, the heart responds by enhancing its contractility, which is the force of contraction of the heart muscle. This phenomenon is explained by the Frank-Starling law of the heart, which posits that the more a heart muscle is stretched with incoming blood (greater preload), the more forcefully it will contract.

This enhanced contractility leads to a more efficient pump function, allowing for improved stroke volume and cardiac output. As such, in response to increased preload, the heart works harder and with greater efficiency by increasing the strength of its contractions, thereby pumping more blood with each heartbeat.

Other options do not accurately represent physiological changes associated with increased preload. For instance, an increase in preload does not typically lead to a decrease in heart rate or systemic vascular resistance. The relationship between preload and diastolic volume is also not direct in that an increase in preload would normally imply increased diastolic volume but is focused more on the muscular response and output rather than a static measurement. Thus, increased contractility is the primary physiological change that occurs in response to heightened preload.