The purpose of this study is to measure blood levels of TXA in children having cardiac surgery which requires cardiopulmonary bypass. TXA is used to reduce bleeding during surgery. This study will help determine if the current dosing of TXA results in therapeutic blood levels.

Inclusion Criteria:

• congenital heart disease requiring surgical repair with cardiopulmonary bypass

Exclusion Criteria:

• children weighing over 20 kg
• family does not want to participate in the study

Children with congenital heart defects having cardiac surgery requiring cardiopulmonary bypass