What is the possible timing of repair of av canal defect with tetralogy of fallot in a child aged 3 months?

depends:: As long as the child grows and gains weight, many cardiologists will put off surgery to make it technically easier and safer on the larger child.

Soon: Anatomy can differ greatly, and there can be complicating issues, but anytime in the next few months would be typical. This is assuming the child was not premature, or have other serious health issues.