During cardiopulmonary bypass (CPB) after heart surgery, a child's blood is exposed to many foreign entities. These conditions trigger the body's inflammatory response which results in leaky capillaries, increased swelling and possibly organ dysfunction. Since the early 1990's, modified ultrafiltration (MUF) has been shown to decrease excess swelling, reduce bleeding, improve heart function, and decrease hospital length of stay. Angiopoietins are a family of proteins necessary for both normal and abnormal blood vessel formation. They also appear to play a role in capillary leak. Though MUF has been shown to improve clinical outcome following CPB, there continues to be conflicting reports whether this is a result of the filtration of inflammatory proteins or simply from excess fluid removal. Since angiopoietins appear to play a role in both inflammation and capillary leak, the investigators hypothesize that the benefit seen after MUF is also secondary to its ability to filter out these proteins, especially angiopoietin-2.

During cardiopulmonary bypass (CPB) for corrective or palliative congenital heart surgery, a child's blood is subjected to hemodilution, hypothermia, nonpulsatile blood flow and exposure to foreign and non-endothelialized surfaces. These non-physiologic conditions trigger the host's innate systemic inflammatory response which results in capillary leak, increased total body water and can lead to end organ dysfunction. Since the early 1990's, modified ultrafiltration (MUF) has been shown to decrease excess tissue edema, reduce postoperative bleeding, improve cardiac contractility, maintain hemodynamic stability, and decrease hospital length of stay. Angiopoietins are a family of vascular growth factors necessary for both normal and abnormal blood vessel formation and appear to play a role in capillary leak. Though MUF has been shown to improve clinical outcome following CPB, there continues to be conflicting reports whether this is a result of the filtration of inflammatory cytokines or simply excess fluid removal. Since angiopoietins appear to play a role in both inflammation and capillary leak, the investigators aim to determine whether MUF's clinical benefit is also secondary to its ability to filter out these molecules, more specifically angiopoietin-2.

Inclusion Criteria:

• Pediatric patients with congenital heart disease undergoing surgical intervention requiring cardiopulmonary bypass and modified ultrafiltration.

Exclusion Criteria:

• Any patients with congenital heart disease who will not require modified ultrafiltration.

Patients with congenital heart disease, undergoing surgical intervention requiring cardiopulmonary bypass and modified ultrafiltration will be recruited.