This is a novel preliminary study of biomarkers of pathologic pre-operative pulmonary vascular development, elevated pre-operative Pulmonary Vascular Resistance Index (PVRi), and complications associated with decreased post-operative pulmonary blood flow in single ventricle patients undergoing superior cavo-pulmonary anastomosis (SCPA). The study will utilize a combined targeted and untargeted approach to both optimize translation of a promising existing biomarker and efficiently identify novel biomarkers and potential therapeutic targets in this population.

Overall Hypothesis: Endothelin-1 (ET1) and associated dysregulation of key metabolic pathways decrease pre-operative pulmonary blood vessel development and increase post-operative pulmonary blood vessel resistance leading to decreased pulmonary blood flow in patients undergoing SCPA.

For enrolled patients, collected data will include:

• 3 mL blood sample (x2) at pre-SCPA catheterization.
• 3 mL blood samples at 2, 24, and 48 hours post-operative.
• Urine sample pre-operatively and post-operatively
• Collection of otherwise-discarded operative tissue sample from the pulmonary artery.
• Collection of clinical data, demographic data, and results of routine, post-operative hemodynamic monitoring.

Inclusion Criteria:

• Congenital heart disease patients undergoing catheterization for pre-SPCA evaluation or undergoing SCPA without plans for cardiac catheterization (utilizing data from a previously performed clinical catheterization).
• All patients will have age from 31 days to 2 years.

Exclusion Criteria:

• Patients who will remain post-op with a pulsatile source of pulmonary blood flow in addition to the cavo-pulmonary anastomosis (so called "1.5 ventricle" repair) will be excluded.
• Due to limitations in acceptable sample blood volumes for research, patients with weight <4kg will be excluded.
• Patients will not be excluded on the basis of gender, ethnicity, genetic diagnosis, gestational age at birth, non-cardiac comorbidity, or pre-operative medication regimen.

Infants with single ventricle heart disease undergoing trans-catheter evaluation in anticipation of superior cavo-pulmonary anastomosis.