The amount of blood pushed out from the heart in one stroke is called:

Question

Accepted Answer

The correct option is (2):
The term for the amount of blood pumped out of the heart's ventricle in a single beat or 'stroke' is precisely defined as **Stroke Volume (SV)**. This is a fundamental concept in cardiovascular physiology and is a crucial indicator of the heart's mechanical efficiency. Stroke volume is calculated as the difference between the End-Diastolic Volume (the volume of blood in the ventricle just before contraction) and the End-Systolic Volume (the blood remaining in the ventricle after contraction). A higher stroke volume, especially in trained athletes, signifies a strong, efficient heart muscle that can eject a large quantity of blood with minimal effort, which is a major physiological goal of endurance training.

The incorrect option is (1):
Cardiac output (CO) is a related but distinct measurement; it represents the *total* volume of blood pumped by the heart per minute, not per single stroke. It is mathematically calculated by multiplying the Stroke Volume (SV) by the Heart Rate (HR). Therefore, while Stroke Volume is a *component* of Cardiac Output, it is the output over sixty seconds, not the output of one single contraction. Understanding the difference between these two measures is essential for analyzing overall circulatory capacity and the heart's performance over time.

The incorrect option is (3):
Residual volume is a term that refers exclusively to the respiratory system, not the circulatory system. It is defined as the volume of air that remains in the lungs and airways even after the most forceful expiration. This volume ensures that gas exchange can continue between breaths and prevents the lungs from completely collapsing. Since this term pertains entirely to pulmonary mechanics and lung capacity, it is wholly inaccurate when describing a measurement of blood volume ejected by the heart.

The incorrect option is (4):
Heart sound refers to the characteristic 'lub-dub' noises produced during the cardiac cycle, which are caused by the forceful closing of the heart's valves. The 'lub' (S1) is the sound of the atrioventricular valves closing, and the 'dub' (S2) is the sound of the semilunar valves closing. These are auditory events used by medical professionals to assess the proper mechanical action of the heart. As heart sounds are an acoustic, qualitative observation and not a volumetric, quantitative measure, they do not describe the *amount* of blood ejected.