The first surgery my son had was called the PA Band surgery. PA stands for Pulmonary Atery.
The doctor described my sons situation using a sponge as a metaphore. Imagine that the lungs are a sponge. They soak up the blood as it comes through, giving it oxygen as it passes. Now let’s pretend the Pulmonary Artery is a water hose being held up to the sponge. If you were to turn on the hose full blast, the sponge would get soaked and be unable to catch the water coming through the hose and it would just start spraying everywhere. In a healthy body, the blood flows through the lungs in a rate that will not overwhelm them. In my son’s body, the blood would be like that hose up to a sponge and the lungs would be ineffective and become damaged, at the very least, causing him to drown at the worst.
During his first surgery they put a band on his Pulmonary Artery in order to restrict the blood flowing to his lungs and hopefully keep them from becoming damaged. This surgery required they open his chest cavity to access his heart, but his heart and the surrounding arteries were left intact. They placed a small band only on the top of his heart, around the pulmonary artery. After that he was closed back up and sent to the PICU.
They very closely monitored the PA band over the next few months for a few reasons. The chances of it sliding were fairly small but if it were to slide too far or in the wrong direction it could have required another surgery to fix. Secondly, as my son grew, so did his heart and the artery. If he grew too big for the PA band it would cause the exact opposite of the intended result; the baby wouldn’t be getting enough blood to oxygenate instead of too much.
This surgery is actually a fairly common surgery for children with heart defects to have. This buys the doctors more time so the child can grow bigger. A larger size allows doctors to see better, see how the heart is going to function outside the womb and possibly allow the heart to repair smaller issues without intervention.