Atrial septal defect · a hole between the upper chambers
Someone said that to me too. I spent months frightened and confused before anyone explained it plainly. This is everything I wish I'd been handed that first day.
In plain words
Your heart has four rooms. The two at the top are separated by a thin wall called the septum. An atrial septal defect means that wall didn’t finish closing — so there’s an opening between them.
Nothing is leaking out of your body. Nothing is torn. Your heart is doing extra laps, not falling apart. Many people carry one for decades without knowing.