Cardiopulmonary bypass (CPB) increases the risk of acute respiratory distress syndrome (ARDS) due to endothelial cell (EC) barrier dysfunction. However, the specific role of mitochondrial N-formyl peptides (mtNFPs) in ARDS following CPB remains unexplored. Here, we investigated the differential expression of circulating mtNFPs in patients after CPB, focusing on the novel role of FPR2 in ECs. Levels of circulating mtNFPs were assessed using enzyme-linked immunosorbent assay (ELISA). Several mtNFPs (ND4, ND5, ND6, and Cox1) were significantly upregulated in patients with ARDS at day 1 post-CPB compared to patients without ARDS. Higher levels of ND6 were correlated with worst PaO