In an atrial septal defect, the left-to-right shunt increases blood volume in which chamber, potentially leading to right-sided heart failure?

• A. Right ventricle
• B. Right atrium
• C. Left atrium
• D. Left ventricle

Answer: (B)

The essential idea is that a left-to-right shunt at the atrial level dumps oxygenated blood from the left atrium into the right atrium. This directly increases the volume load on the right atrium, making it the chamber that enlarges first due to the extra incoming blood. As this excess blood continues to circulate, the right ventricle also handles more volume, which can lead to right-sided dilation and eventually right-sided heart failure if the shunt is large or long-standing. The left-sided chambers aren’t receiving this additional volume from the shunt, so they’re not the primary sites of increased blood volume in this scenario.