Hypoplastic left heart syndrome (HLHS) is a severe form of congenital heart disease that consists of multiple obstructions to flow through the left heart and aorta, as well as hypoplasia of the left ventricle. Most patients require a three-stage surgical protocol starting within days of birth. Stage I of this process is the Norwood reconstruction (within the first few days of life), Stage II (usually required within 3-8 months) involves creation of a direct connection between the patient's superior vena cava and the pulmonary arterial confluence (bidirectional Glenn anastomosis), and the last stage is creation of a Fontan circulation (typically within the first 2-4 years). This "single ventricle" approach requires the right ventricle to perform as the only circulatory pump for the entire body.

Our long-term goal is to develop regenerative strategies to strengthen and augment the right ventricular muscle of the single-ventricle heart following surgical palliation in HLHS patients. To determine the safety and feasibility of a cell-based therapeutic intervention at the Stage II surgery, we aim to document the natural history of post-surgical care in HLHS patients having undergone standard of care with protocol specific follow-up over the course of a 6-month period.

This prospective study will document the natural history in patients with HLHS after planned Stage II surgical palliation with a focus on cardiovascular parameters within 6 months following surgery in 10 patients.

Inclusion Criteria:

• Individuals with HLHS having undergone Stage I surgical palliation and undergoing planned Stage II palliative Glenn surgery.
• Individuals up to 18 months of age are eligible if written informed consent can be obtained from both parents and/or legal guardians, unless one parent is not reasonably available.

Exclusion Criteria:

• Severe chronic diseases, extensive extra-cardiac syndromic features, or history of cancer

The following complications of congenital heart disease:

• Any condition requiring urgent, or unplanned procedure within 15 days prior to Stage II surgical repair.
• Severe pulmonary hypertension (reported in the medical record as >70% systemic pressure).
• Other clinical concerns as documented by a site investigator that would predict (more likely to happen than not to happen) a risk of severe complications or very poor outcome during or after Stage II surgical repair.

Children with HLHS up to 18 months of age requiring a planned Stage II bi-directional Glenn surgery