This study is designed to learn more about children who have blockage of the left side of their heart. The goal is to determine how much the heart muscle has thickened before surgery and how it changes in the months after surgery. Investigators are also looking for blood tests that may help them predict which patients will have the most thickening pre-operatively and the best return towards normal after surgery. The findings of this study will help the investigators develop new tests to monitor affected patients and develop new therapies to help minimize heart thickening.

Inclusion Criteria:

• Congenital heart disease patients with the following diagnoses undergoing surgical repair: Coarctation of the aorta (CoA), aortic stenosis (AS), subaortic membrane (sub-AS), supravalvar aortic stenosis (supra-AS).
• All patients will have age from birth through 18 years of age.
• While we will generally not enroll patients with other co-morbid heart disease that would alter the cardiac physiology (see exclusion criteria), patients with patent foramen ovale, atrial septal defect, and patent ductus arteriosus specifically will be allowed.

Exclusion Criteria:

• Patients with lesions not listed in inclusion criteria (including but not limited to hypoplastic left heart syndrome, Shone's complex, mitral valve stenosis or regurgitation greater than trivial, non-restrictive ventricular septal defect, interrupted aortic arch, atrio-ventricular canal defect)
• Corrected gestational age at time of surgery <34 weeks
• Weight at time of surgery <2000g.
• Patients who will not be seen for any follow-up care at Children's Hospital Colorado

Potential subjects will be identified from the cardiac surgical and clinic schedules at Children's Hospital Colorado (CHCO).