Absolutely! Congenital cardiac defects frequently deprive the developing brain of oxygen and result in microcephaly (hlhs) and/or distinct areas of brain infarction. It is rather common for infants affected by such defects to demonstrate neurodevelopmental delay of varying degree as they grow older. Repetitive major cardiothoracic surgeries do little to protect the already vulnerable brain in such cases.
Variable. If you focus on cause and effect, the issue is complex. The heart is responsible for providing the brain with adequate oxygen/nutrients to develop & function, so a defect that does not may impair those parameters. One of the more significant impacts is the degree that repeated hospitalization/surgery can have on a kids access to learning at opportune times. Simple defect=no,complex + surgeries=yes.