Define cardiac output.

• A. The volume of blood in the ventricles after diastole.
• B. The amount of blood pumped by the left ventricle in 1 minute.
• C. The number of heartbeats per minute.
• D. The total blood volume in the circulatory system.

Answer: (B)

Cardiac output is the volume of blood the heart ejects into the circulation each minute. It’s determined by how many times the heart beats per minute (heart rate) and how much blood is ejected with each beat (stroke volume), so CO = HR × SV. This means CO specifically measures the heart’s pumping performance over a minute, typically assessed by the left ventricle for systemic circulation. For example, a resting heart rate of about 70 beats per minute with a stroke volume around 70 mL per beat yields roughly 5 liters per minute. This distinguishes it from the other options: the end-diastolic volume is the amount of blood in the ventricle after filling, heart rate alone is just the beats per minute, and total blood volume is the entire amount of blood in the circulatory system, not the amount the heart pumps per minute.