Overview of the study workflow. Study procedures will occur in a one- or two-day visit. Upon arrival for testing, formal consent for participation will be obtained. Assessment of arterial stiffness, endothelial function, and blood sampling for biomarkers will be done while fasting. Cardiopulmonary stress test will be performed on the same day. CMR and ambulatory blood pressure monitoring (ABMP) will be arranged for the same or for the following day. When the study tests cannot be completed at the first visit, they will be completed within 3 months of the first visit. The study protocol was approved by the Institutional Review Board or Institutional Ethics Committee at each participating center, and informed consent and assent will be obtained, depending on age, from patients and their parents/legal guardians before trial enrollment.