Which description best characterizes afterload?

• A. The time interval between heartbeats
• B. The preload before atrial contraction
• C. The diastolic filling period
• D. The pressure the heart must generate during systole to eject blood

Answer: (D)

Afterload is the pressure the ventricle must overcome during systole to eject blood. This load comes from the arterial pressure and vascular resistance the heart pumps against, so the ventricle has to generate a high enough pressure to open the aortic valve and push blood into the arteries. That's why the description that best fits is the pressure the heart must generate during systole to eject blood. It’s not the time between heartbeats (that’s heart rate), not the filling stretch before contraction (preload), and not the diastolic filling period. When afterload increases, the ventricle must work harder to achieve the same stroke volume, which can reduce output if contractility doesn’t compensate.