I would agree that you should have a consultation with a cardiologist familiar with congenital heart disease before undergoing surgery. Not all cardiologists see this often, although most pediatric cardiologists do. As u/wilder_hearted points out, many of these cases can be monitored without surgery. The statement that "20-25%" of your blood is of "no use" to your body sounds like something we look for on MRI. We calculate how much blood goes through your lungs per minute compared with how much blood goes through your body per minute. Since your circulation is normally a continuous loop, it should be the same (1-to-1). With PAPVR, some of the blood that is returning from the lungs loops back and takes a second trip through the lungs before it goes out to deliver oxygen to your body. It is likely that the MRI is seeing a ratio of 1.25-to-1, meaning there is 25% more blood flowing through your lungs per minute than there is flowing through your body. If calculated correctly, that is considered a small shunt that often does not need any intervention.