## **Core Concept**
The stroke volume (SV) or stroke output is the volume of blood pumped by each ventricle of the heart in one contraction. In a normal adult, this value is crucial for understanding cardiac function and overall cardiovascular health.

## **Why the Correct Answer is Right**
The correct answer, , indicates that the stroke volume is approximately 70 mL. This value represents the typical amount of blood ejected by each ventricle with every heartbeat in a healthy adult. The stroke volume is a critical component of cardiac output (CO), which is calculated as CO = SV * heart rate. A normal adult heart rate is about 70-80 beats per minute, making the cardiac output approximately 5 liters per minute.

## **Why Each Wrong Option is Incorrect**
* **Option A:** is incorrect because 40 mL is lower than the normal stroke volume for a healthy adult. While stroke volume can vary based on factors like preload, contractility, and afterload, 40 mL is on the lower side and might be seen in conditions with decreased cardiac function.
* **Option B:** is incorrect because 90 mL is higher than the typical stroke volume for a normal adult. While athletes or individuals with high cardiac output states might have higher stroke volumes, 90 mL is above the average for a healthy adult at rest.
* **Option D:** is incorrect because 100 mL is even higher than option B and is not considered a normal stroke volume for a healthy adult at rest.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that stroke volume can be influenced by the Frank-Starling mechanism, which states that the stroke volume of the heart increases in response to an increase in the volume of blood filling the heart (the end diastolic volume) when all other factors remain constant. This principle is vital for understanding how the heart adapts to changes in blood volume and pressure.

## **Correct Answer:** .