The volume of blood ejected with each heartbeat is called what?

• A. Cardiac output
• B. Stroke volume
• C. Preload
• D. Ejection fraction

Answer: (B)

Stroke volume is the amount of blood the heart pumps out of the ventricle with each beat. It reflects how much blood is ejected per contraction and is influenced by preload (venous return stretching the heart, afterload (the pressure the heart must pump against), and contractility (the strength of heart muscle). Cardiac output, by contrast, is the total blood pumped per minute and equals stroke volume multiplied by heart rate. Ejection fraction is the percentage of the end-diastolic volume that is ejected each beat, not the absolute volume. Preload refers to the initial stretch before contraction, not the actual volume ejected. Normal stroke volume is typically about 60–100 mL per beat, with ejection fraction normally 55–70% in a healthy heart.