This is a study to describe the overall pattern of lung ventilation and perfusion defects in individuals with PASC. Subjects with PASC with a documented history of COVID-19 and persistent symptoms of fatigue, dyspnea, and/or exercise intolerance will complete questionnaires, and undergo pulmonary function tests, 6-minute walk tests, and a low dose CT chest to describe the overall pattern of lung regional ventilation and blood distribution and to compare this pattern to asymptomatic controls with and without prior COVID-19.