Final answer:
Contractility is the potent regulator in the force of contraction in the heart that affects the length-tension relationship.
Step-by-step explanation:
The potent regulator in the force of contraction in the heart that greatly affects the length-tension relationship is contractility. Contractility refers to the force of the contraction of the heart muscle, which controls stroke volume (SV) and impacts end-systolic volume (ESV). The more forceful the contraction is, the greater the SV and smaller the ESV.