Background: Previous research demonstrated an association between low volume fraction of pulmonary vasculature contained in vessels <5mm2 in cross-sectional area (BV5%), assessed using quantitative CT, and worse outcomes in patients with acute COVID-19. The role of the pulmonary vasculature in exercise intolerance in PASC, however, has yet to be determined. Aim: To investigate the relationship between BV5% and oxygen saturation during cardiopulmonary exercise test (CPET) in patients with PASC. Methods: Subjects with PASC presenting for pulmonary rehabilitation were enrolled retrospectively. Subjects received inspiratory chest CT, and performed CPET with oxygen saturation monitoring. Chest CT was post-processed to compute BV5%. Results: 25 patients (5 male, 20 female) were enrolled; mean age 43(SD=12) years. Mean BV5% was 64.88% (SD=3.29%). Median oxygen saturation at ventilatory threshold 2 (VT2) was 98% (range=92-100%). BV5% correlated inversely significantly with saturation at VT2 (R=-0.423; p=0.035). Conclusion: Subjects with PASC were observed to have relatively preserved BV5% in contrast to patients with acute COVID-19 in whom BV5% was observed to be lower(2). A negative correlation was found between BV5% and saturation at VT2 during CPET in patients with PASC. In acute COVID, there is an occlusion of the BV5, resulting in low BV5% and blood shift to larger blood vessels. Hypothesizing that in patients with PASC, the intra-alveolar blood vessels, might be (partially) occluded.  Hence, this shifts the blood to BV5, elevating BV5% and might explain the negative correlation between BV5% and saturation at VT2 in patients with PASC.