## **Core Concept**
Cardiac output (CO) is the volume of blood the heart pumps per minute. It is a critical parameter in cardiovascular physiology and is calculated as the product of heart rate (HR) and stroke volume (SV), i.e., CO = HR × SV. Basal cardiac output refers to the cardiac output under basal conditions, which is a standardized condition of a fasting subject at rest in a supine position.

## **Why the Correct Answer is Right**
The basal cardiac output in an adult is approximately 5 liters per minute (L/min). This value represents the heart's ability to pump blood efficiently under resting conditions. It is calculated using an average heart rate of about 70 beats per minute and an average stroke volume of approximately 70 milliliters per beat. Therefore, CO = 70 beats/min × 70 mL/beat = 4900 mL/min, which is roughly 5 L/min.

## **Why Each Wrong Option is Incorrect**
- **Option A:** 1 L/min is significantly lower than the expected basal cardiac output. This value might be seen in a severely compromised cardiac function or in certain specific conditions but not under normal basal conditions.
- **Option B:** 3 L/min is still lower than the normal basal cardiac output. While cardiac output can vary based on body size and condition, 3 L/min is generally considered low for an average adult under basal conditions.
- **Option D:** 10 L/min is higher than what is typically seen under basal conditions. Cardiac output can increase to this level or even higher during exercise or stress but not under basal conditions.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that cardiac output can vary among individuals based on factors such as body size, age, and physical condition. The cardiac output index (cardiac output per square meter of body surface area) is often used to normalize cardiac output for body size. A normal cardiac output index is about 2.6 to 4.2 L/min/m².

## **Correct Answer:** C. 5 L/min.