The amount of blood ejected from the left ventricle during each beat is the

• A. Cardiac output
• B. A-V O2 difference
• C. Heart rate
• D. Stroke volume

Answer: (D)

Stroke volume is the amount of blood the left ventricle ejects with each heartbeat. It’s a per-beat measure that reflects how much blood is moved into the circulation during one contraction. The left ventricle’s stroke volume depends on preload (venous return and ventricular stretch), contractility, and afterload. In general, about 60–80 mL is pumped per beat at rest in a typical adult, and it can increase with exercise due to greater venous return and stronger contraction.

Cardiac output, by comparison, is the total volume pumped per minute and equals stroke volume multiplied by heart rate. Heart rate is simply the number of heartbeats per minute. The arterial-venous oxygen difference is the amount of oxygen extracted by the tissues, not a measure of how much blood the heart ejects.

So the term that matches “the amount of blood ejected from the left ventricle during each beat” is stroke volume.