Capacitance vessels affect the heart by:

• A. They reduce stress on the heart.
• B. They increase cardiac output directly
• C. They hasten heart rate
• D. They raise systemic vascular resistance

Answer: (A)

Capacitance vessels, mainly the veins, are highly compliant and act as a reservoir for blood. Their ability to hold more blood with only small rises in pressure buffers swings in venous return to the heart, keeping preload from spiking. By smoothing preload and reducing abrupt increases in ventricular wall stress, they lower the work the heart must perform and, consequently, the myocardial oxygen demand. That is why they reduce stress on the heart. These vessels don’t directly boost cardiac output, don’t inherently speed the heart rate, and they don’t raise systemic vascular resistance (that’s mainly the arterioles and arterial tone).