How is stroke volume defined?

Stroke volume is defined as the volume of blood the heart ejects with each beat. This measure is a critical component of cardiac function and is an important determinant of how effectively the heart can supply blood to meet the body's demands during rest and physical activity. Stroke volume is influenced by several factors, including the length of the cardiac muscle fibers at the end of diastole (preload), the degree of muscle contraction (contractility), and the resistance the heart must overcome to eject blood (afterload).

Understanding stroke volume is essential for assessing cardiovascular health and the efficiency of the heart's pumping action. When evaluating exercise capacity or training adaptations, changes in stroke volume can indicate improvements in cardiovascular fitness.

In terms of the other choices, the first option refers to the amount of blood the heart receives, which relates more to venous return rather than the output per heartbeat. The third choice mentions the total amount of blood in the body, which is not directly related to the stroke volume, as this is a broader measure of blood volume rather than output. Lastly, the fourth option describes the volume of blood pumped by the lungs, which relates to pulmonary circulation but does not define stroke volume, as stroke volume is specifically about the blood ejected by the heart.