atrial septal defect
An atrial septal defect is a hole in the wall that separates the two upper chambers of the heart, the atria. Picture a duplex apartment with a shared wall between two rooms: if there is an opening in that wall, air can drift from one room to the other. Here, blood that should stay on the left side leaks across into the right side because the dividing wall is incomplete.
Because the left atrium normally runs at a slightly higher pressure than the right, oxygen-rich blood is pushed from left to right through the hole. This extra volume cycles uselessly back through the right heart and the lungs, gradually overworking them. Small defects may cause no symptoms for decades, while larger ones can lead to an enlarged right heart, irregular rhythms, and breathlessness in adulthood.
Many atrial septal defects are quiet and discovered only when a doctor hears a soft murmur or when imaging is done for another reason. Sizable defects are now often closed with a catheter-delivered device rather than open surgery, restoring normal flow and preventing later complications.
A woman in her forties with new palpitations and a fixed split second heart sound is found to have an atrial septal defect with an enlarged right ventricle, prompting device closure.
A fixed, widely split second heart sound is a classic clue to atrial septal defect.
An atrial septal defect differs from a patent foramen ovale: the foramen ovale is a normal fetal flap that simply fails to seal, whereas a true atrial septal defect is genuinely missing septal tissue.