What is defined as cardiac output?

Cardiac output is fundamentally defined as the total amount of blood that the heart pumps out per minute. This measurement is crucial in understanding how effectively the heart is functioning to supply oxygen and nutrients to body tissues. It is calculated as the product of stroke volume (the amount of blood ejected with each heartbeat) and heart rate (the number of beats per minute). Thus, the concept of total blood ejected aligns perfectly with the definition of cardiac output.

The other options do not accurately reflect this definition. For instance, while blood volume in the heart contributes to overall circulatory function, it does not equal the output; it is simply a reflection of the filling of the heart, not the ejection rate. Similarly, the amount of blood returning to the heart is important for heart function but refers to venous return, which is distinct from cardiac output. Lastly, multiplying heart rate by blood pressure does not directly provide a measure of cardiac output and can be misleading, as blood pressure and cardiac output are related but separate values in cardiovascular physiology. Thus, the choice that addresses the total volume of blood ejected per minute correctly captures the essence of cardiac output.