This sounds to me like a "hole" that has been made in the aorta during the corrective surgery for this congenital malformation (VSD). It is not possible to be sure without seeing more context. Consider "defect in the aorta"
Congenital heart defect corrective surgeries: MedlinePlus Medical ...
www.nlm.nih.gov/medlineplus/ency/article/002948.htm
The pulmonary arteries are separated from the aortic trunk, and any defects are patched. Usually, children also have a ventricular septal defect, and that is also