The peripheral resistance against which the ventricle is contracting as it pushes blood into the aorta is referred to as _____.

• A. Afterload
• B. Preload
• C. Contractility
• D. Ejection fraction

Answer: (A)

Afterload is the pressure the ventricle must generate to push blood into the aorta, effectively the resistance the heart works against during systole. This peripheral resistance comes from systemic vascular resistance and the pressure in the aorta that opposes ejection. Because the ventricle has to overcome this pressure to open the aortic valve and propel blood forward, afterload directly determines how hard the heart must contract to achieve stroke volume. This is distinct from preload, which is about filling and the stretch of the ventricles before contraction; contractility, the intrinsic strength of the heart muscle; and ejection fraction, the proportion of filled volume ejected with each beat. When afterload rises, stroke volume tends to fall unless contractility or heart rate increases to compensate, making afterload the key concept here.