To safely optimize blood testing and costs for pediatric cardiac surgical patients without adversely impacting patient outcomes. This is a quality improvement cohort project with pre- and postintervention groups. University-affiliated pediatric cardiac ICU in a tertiary care children's hospital. All patients were surgical patients for whom Risk Adjustment for Congenital Heart Surgery categories allowed for stratification by complexity. The preintervention group was treated in 2010 and the postintervention group in 2011. Laboratory ordering processes were analyzed, and practice changed to limit standing blood test orders and requires individualized ordering. Three hundred nineteen patients were studied in 2010 and 345 in 2011. Groups were similar in median age, weight, length of stay (ICU length of stay), and Risk Adjustment for Congenital Heart Surgery category. There was a reduction in the total blood tests per patient (24 vs 38; p < 0.0001) and length of stay adjusted tests per patient-day (10.4 vs 14.4; p = 0.0001) in the postintervention group. The largest test reductions were blood gases and single electrolytes. Adverse outcomes, such as extubation failure (6.4% vs 5.6%), central catheter-associated bloodstream infection (2.2 vs 1.5), and hospital mortality (0.6% vs 0.6%), were not significantly different between the groups. Cost analysis demonstrated an overall laboratory cost savings of 32%. In addition, the volume of packed RBC transfusions was also significantly decreased in the postintervention group among the most complex patients (Risk Adjustment for Congenital Heart Surgery, 6). Blood testing rates were safely decreased in postoperative pediatric cardiac patients by changing laboratory ordering practices. In addition, packed RBC transfusion was decreased among the most complex patients.