Which term describes the end-systolic volume's opposing force during contraction?

The term that describes the end-systolic volume's opposing force during contraction is afterload. Afterload refers to the pressure the heart must work against to eject blood during systole—essentially the "load" that the ventricles must overcome to pump blood into the arteries.

In the context of the heart's function, when the left ventricle contracts during systole, it must generate enough pressure to overcome both the aortic pressure and the resistance in the systemic circulation to effectively eject blood. Higher afterload can create a situation where the heart has to work harder to achieve this ejection, which can lead to various forms of cardiac strain if the workload exceeds the heart's capacity.

Preload, on the other hand, pertains to the initial stretching of the cardiac muscle fibers at the end of diastole, and is determined largely by the venous return and filling of the ventricles. Cardiac output is a measure of the volume of blood the heart pumps in a minute and relates to both heart rate and stroke volume but does not directly describe the opposing force during contraction. Contractility refers to the intrinsic ability of heart muscle fibers to contract and is influenced by various physiological factors.

Therefore, understanding afterload is critical for assessing the mechanical workload