Cardiac Output is defined as which of the following?

• A. Cardiac Output
• B. Stroke Volume x Heart Rate
• C. Heart Rate x Stroke Volume
• D. Total Blood Volume

Answer: (C)

Cardiac Output is the amount of blood the heart pumps per minute, a flow rate. It’s determined by two factors: how often the heart beats (heart rate) and how much blood is ejected with each beat (stroke volume). Multiply these two—heart rate (beats per minute) by stroke volume (milliliters per beat)—to get the volume pumped per minute. The standard expression is heart rate × stroke volume, which equals cardiac output; the order doesn’t change the result because multiplication is commutative, but this is the conventional form used in physiology. For example, with a heart rate of 70 beats per minute and a stroke volume of 70 mL per beat, the cardiac output is about 4900 mL per minute (roughly 5 L/min). Total blood volume, on the other hand, is the amount of blood present in the circulatory system at any given time, not the rate of blood flow, so it’s not cardiac output.