FUVID Study: Functional Characterization of Children With Chronic Venous Thromboembolic Disease

Subjects will be identified from the clinical setting and approached to participate in this observational study where participants will be enrolled at 3 different sites and referred from several more sites and have: cardiopulmonary exercise testing and pulmonary function testing at The Institute of Exercise and Environmental Medicine (IEEM), UTSW Exercise Facility, Cardiac MRI and MRI for pulmonary perfusion at Children's Medical Center and MR Spectroscopy and MR for Muscle Perfusion at the Advanced Imaging Research Center (AIRC) performed in Dallas over a 3 day research visit at week 12 and Month 12. Blood is collected for biomarkers at these visits and multiple questionnaires are completed by participants.