Baby fetus 8 months old - is it normal to have a "shunt"? Can anyone help explain?

At my last ecograph (done twice with two different specialists) I was
told that everything was normal. However, we made a movie of the
entire examination and I found out my baby's heart has one extra
"opening" - a shunt I'd say - the existence of this supplementary
opening has been confirmed by the doctors who said it was "normal" but
I am not a doctor and it really looks to me like a ventricular shunt.

My question is: would this extra opening be normal as the two doctors
told me? They explained that the blood does not flow through the lungs
and so it needs to flow through this extra opening inside the heart.
If it is normal, when does it close then?

Can someone help me with me a better explanation?
Thank you so much for helping me understand.