What is the primary determinant of afterload?

• A. Systemic vascular resistance (arterial pressure)
• B. Heart rate
• C. Venous return
• D. Diastolic filling time

Answer: (A)

Afterload is the pressure the ventricle must overcome to eject blood during systole. The key determinant of this opposing pressure is systemic vascular resistance, which together with arterial pressure sets how hard the heart has to contract to open the aortic valve. When arterial pressure is high due to increased systemic resistance, the ventricle must generate a higher systolic pressure, increasing afterload. Heart rate mainly affects the rate of blood flow and myocardial oxygen demand rather than the pressure the ventricle faces to eject blood. Venous return influences preload (the filling pressure before contraction), not the resistance the heart must overcome during ejection. Diastolic filling time also affects preload, not the pressure against which the ventricle must push. Therefore, systemic vascular resistance (arterial pressure) is the primary determinant of afterload.