Will a child's weight increase after having asd surgery?

Possibly: An ASD repair will not cause an otherwise healthy child to gain weight. Rarely a child with an ASD will have significant enough heart failure that weight gain is slow. In those cases, repairing the ASD will restore normal weight gain.

Catch up likely: If a kids ASD was holding back his growth rate, fixing the problem would result in more available energy for growth. Catch up growth over the next months & years would be expected. If it were a small defect with minimal growth effect, it might not matter.

Possibly: An ASD usually does not cause heart failure. The repair is performed to prevent future problems. Rarely an ASD will cause heart failure and in that circumstance repair may improve growth.

It May: The answer depends on whether the poor weight gain was from the ASD or another cause. If from the asd, then yes, the child should gain better weight. But, obviously, if the problem were due to another source, then likely not.