What is defined as the amount of blood left in the ventricles at the end of systole?

The correct choice refers to the end-systolic volume, which is specifically defined as the amount of blood that remains in the ventricles after they have completed the contraction phase of the cardiac cycle, known as systole. During systole, the ventricles contract to pump blood out of the heart, and the volume that remains afterwards is crucial for understanding heart function and efficiency.

This measurement is significant in assessing cardiac health, as it helps to quantify how much blood is not ejected with each heartbeat, impacting overall heart performance and potentially indicating conditions such as heart failure if volumes are abnormally high.

In contrast to this concept, stroke volume refers to the amount of blood pumped by the ventricles with each heartbeat, end-diastolic volume is the amount of blood in the ventricles at the end of diastole (just before contraction), and cardiac output is the total volume of blood pumped by the heart per minute. Each of these terms serves a different purpose within the cardiovascular physiology context, highlighting the significance of measuring in different phases of the cardiac cycle.