Final answer:
The greatest end-systolic volume (ESV) occurs when there is increased parasympathetic stimulation of the heart, which decreases the force of contraction and stroke volume, leading to more blood being left in the ventricle after systole.
Step-by-step explanation:
The end-systolic volume (ESV) is the amount of blood remaining in each ventricle after systole, which is the phase of the heartbeat when the heart muscle contracts and pumps blood from the chambers into the arteries. The question is concerned with the situation that would result in the greatest ESV. According to cardiovascular physiology, an increase in parasympathetic stimulation would lead to an increase in ESV due to the decrease in the strength of ventricular contractions, which leads to a smaller stroke volume and a consequently larger ESV. On the other hand, sympathetic stimulation, being a positive inotrope, increases the strength of these contractions, resulting in a larger stroke volume and a smaller residual ESV. Therefore, the answer to the question is (a) When parasympathetic stimulation of the heart is increased, as this would result in the heart pumping less blood out during a contraction, leaving a greater volume of blood in the ventricle at the end of systole.