What impact does increasing venous return have on the intensity of murmurs?

Increasing venous return enhances the volume of blood returning to the heart, which in turn raises the preload, or the initial stretching of the cardiac muscle fibers prior to contraction. This increase in preload leads to greater stroke volume and often higher blood flow across the valves.

Murmurs are caused by turbulent blood flow, which can occur due to narrowed valves, regurgitant flow, or increased flow across normal valves. When venous return increases, there is a greater volume and velocity of blood flow. This heightened turbulence intensifies the sound of murmurs, making them more pronounced.

This principle applies to murmurs of both normal valves experiencing higher blood flow and those associated with valvular pathology, as turbulence increases with improved flow dynamics. Thus, the intensity of murmurs generally increases when venous return rises, making the choice indicating that all murmurs' intensity increases accurate in this context.