Acute coronavirus disease 2019 (COVID-19) infection can include cardiac and pulmonary manifestations as well as post-infectious complications such as multisystem inflammatory syndrome (MIS-C), also known as pediatric inflammatory multisystem syndrome (PIMS / PIMS-TS). The precise etiology for COVID-19 symptoms and MIS-C is still obscure but there is evidence that endothelial damage may play a role. At recovery, symptoms such as dyspnea, fatigue, weakness, myalgia, chest pain and palpitations are prevalent. Data regarding functional capacity, cardiopulmonary and vascular function post COVID-19 infection are scarce. To the best of our knowledge, few studies has evaluated functional capacity of patients recovering from COVID-19 infection and complications using cardiopulmonary exercise testing (CPET), and no study included endothelial function assessment. Aims I. To investigate the effect of COVID-19 infection on cardiovascular and pulmonary function and exercise parameters in the pediatric and adult population. II. To investigate the effect of PIMS on endothelial function in pediatric population. Research hypothesis: 1. After COVID-19 infection, aerobic function is impaired due to cardiac and/or pulmonary limitation 2. Endothelial function in children after PIMS is impaired in comparison to healthy individuals and to patients after COVID infection with mild symptoms. Importance of the study: Cardiovascular and pulmonary assessment of patients recovering from COVID-19 infection using CPET and Peripheral Arterial Tonography (EndoPAT™) has not been reported previously, and will provide new insights into the long term significance of COVID-19 infection.