RecruitingDiagnostic testPathophysiologic Mechanism for Arrhythmias and Impaired Aerobic Capacity in Tetralogy of Fallot and Other Congenital Heart DiseasesThis study is being done to determine the mechanism(s) contributing to the onset of symptoms (i.e. shortness of breath and/or palpitations) as well as changes in heart structure in patients with congenital heart disease (CHD)