Regenerative therapies could provide new ways of treating heart failure. Unlike many organs in the human body, such as the skin and the GI tract, the ability to regenerate heart muscle decreases after birth, but the precise timing of this decrease and how this decrease is altered in heart disease are uncertain. The investigators will use an innovative approach to quantify cellular heart regeneration in pediatric patients, an appropriate population for determining this decline as well as the potential for reactivating heart muscle regeneration.

The study has now been registered on ClinicalTrials.gov, despite its initiation on July 23, 2015, as registration was not mandated at the original study site, the University of Pittsburgh Medical Center. However, following the transfer of the study to Weill Cornell Medicine, adherence to institutional requirements necessitated its registration on ClinicalTrials.gov.

Inclusion Criteria:

• Patients at 30 days of age to 1 year of age undergoing scheduled elective cardiac surgery will be eligible for study inclusion.
• The investigators will recruit patients at 30 days of age to 1 year of age with those types of heart disease whose surgical approach has a high probability of myocardial resection.
• Diagnosis of ToF/PS or other types of heart disease that have a high likelihood of requiring surgery that involves routine resection of myocardium that becomes available for research

Exclusion Criteria:

• Patients with low chance of having resection of myocardium as part of their surgical care.