Inclusion Criteria:

• Diagnosis of a congenital heart defect with functionally single right ventricle (such as HLHS, HLHS variants, unbalanced AV septal defect with RV dominance, DORV with Hypoplastic LV) undergoing Fontan surgical palliation.
• At least 2 and less than or equal to 5 years of age at time of Fontan surgical palliation.
• For subjects enrolling in the treatment arm, previous participation in clinical trial Umbilical Cord Blood Collection and Processing for Hypoplastic Left Heart Syndrome Patients (NCT01856049) with autologous UCB-MNC product collected and available for distribution is required.

Exclusion Criteria:

• History of DMSO reaction (treatment arm only subjects).
• Parent(s) or legal guardian unwilling to have their child participate or unwilling to follow the study procedures.
• Severe chronic diseases at the discretion of the treating physician.
• Extensive extra-cardiac syndromic features.
• History of cancer.
• Any of the following complications of his/her congenital heart disease:
  • Any condition requiring urgent, or unplanned interventional procedure within 15 days prior to Fontan surgical palliation, unless complete and full cardiac recovery is documented by site investigator.
  • 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, not directly related to the stem cell product or its injection procedure, during or after Fontan surgical palliation.
• Individuals with severe heart failure that requires heart transplantation.
• Individuals with refractory or worsening arrhythmia.
• Individuals with an automated implantable cardioverter defibrillator (AICD) or pacemaker.
• Patients with prior surgical complications during the Fontan surgical palliation that resulted in or could be reasonably expected to significantly decrease cardiac function.