Capacitance vessels influence cardiac workload by:

• A. Increasing systemic vascular resistance
• B. Reducing stress on the heart
• C. Directly changing stroke volume
• D. Elevating heart rate

Answer: (B)

Capacitance vessels regulate venous return and preload, which largely determines how hard the heart has to work. Veins serve as a large reservoir that holds most of the circulating blood at low pressure. When venous capacitance increases, more blood is pooled in the veins and less returns to the heart, lowering end-diastolic volume and pressure. This reduces ventricular wall tension and the energy the heart must expend to eject blood, thus decreasing myocardial workload. In contrast, changes that would raise venous return (venoconstriction) can increase preload and raise workload, but the primary effect of capacitance vessels is to buffer and reduce the heart’s stress by lowering preload.