Final answer:
Congestive heart failure in a patient with significant mitral regurgitation occurs because of increased pressure in the left atrium.
Step-by-step explanation:
In a patient with significant mitral regurgitation, congestive heart failure occurs because of increased pressure in the left atrium. Mitral regurgitation is a condition where the mitral valve does not close properly, allowing blood to leak back into the left atrium instead of flowing forward into the left ventricle. This causes an increase in pressure in the left atrium, leading to congestion and fluid buildup.