If i had a heart defect, what is the risk my children might have one?

Depends: It depends on what the defect is and if you have any other congenital conditions that go along with it. It's hard to make a global statement for all heart defects. You're correct, though, that it is something to consider - some defects do have a familial preponderance although rarely 100%.

General risks: The listed basic risk from parent to child is 4% for ANY (not just the same) heart defect which doubles if the other parent has any form of defect. There are some rare genetic syndromes which have a heart defect as part of the process, and that risk depends on the inheritance pattern of the syndrome.