Regurgitation of blood through a prolapsed mitral valve may cause __________ pressure in the __________ atrium.

Regurgitation of blood through a prolapsed mitral valve significantly affects pressure dynamics within the heart. A prolapsed mitral valve enables blood to flow backward from the left ventricle into the left atrium during systole (when the ventricles contract). This backward flow causes an increase in volume within the left atrium, leading to higher pressure in that chamber.

The left atrium serves as the receiving chamber for oxygenated blood returning from the lungs, and when there's regurgitation, this can result in elevated pressure due to the accumulation of blood. Over time, if this condition persists, it could lead to complications like atrial enlargement or even atrial fibrillation. Therefore, the correct answer highlights the direct consequence of mitral valve prolapse and the resultant blood flow dynamics impacting the pressure within the left atrium.