Which statement best describes right and left heart compliance and its effect on cardiac output when filling pressures are equal?

Which statement best describes right and left heart compliance and its effect on cardiac output when filling pressures are equal?

• A. The right ventricle is more compliant and yields a higher cardiac output than the left under equal filling pressure.
• B. The left ventricle is more compliant and yields a higher cardiac output than the right under equal filling pressure.
• C. Both ventricles have equal compliance and filling pressure determines output equally.
• D. The right ventricle is stiffer, leading to lower output at the same filling pressure.

Answer: (A)

The key idea here is how ventricular compliance sets preload for a given filling pressure. Compliance is how much volume a ventricle can accommodate per unit of filling pressure (ΔV/ΔP). The right ventricle has a thinner wall and a more compliant myocardium, so for the same filling pressure it can fill with a larger end-diastolic volume. When preload is higher, the Frank-Starling mechanism drives a greater stroke volume and thus a higher cardiac output, assuming contractility remains similar. In contrast, the left ventricle is stiffer (less compliant) because of its thick, muscular wall. At the same filling pressure, it cannot fill to the same end-diastolic volume, so its stroke volume and cardiac output are lower under those equal-pressure conditions. That’s why the statement describing the right ventricle as more compliant and capable of higher output under equal filling pressures best fits physiology. The alternatives imply the left is more compliant or that both are equal in compliance, which contradicts the known differences in ventricular filling properties.

The key idea here is how ventricular compliance sets preload for a given filling pressure. Compliance is how much volume a ventricle can accommodate per unit of filling pressure (ΔV/ΔP). The right ventricle has a thinner wall and a more compliant myocardium, so for the same filling pressure it can fill with a larger end-diastolic volume. When preload is higher, the Frank-Starling mechanism drives a greater stroke volume and thus a higher cardiac output, assuming contractility remains similar.

In contrast, the left ventricle is stiffer (less compliant) because of its thick, muscular wall. At the same filling pressure, it cannot fill to the same end-diastolic volume, so its stroke volume and cardiac output are lower under those equal-pressure conditions.

That’s why the statement describing the right ventricle as more compliant and capable of higher output under equal filling pressures best fits physiology. The alternatives imply the left is more compliant or that both are equal in compliance, which contradicts the known differences in ventricular filling properties.