Postural orthostatic tachycardia syndrome (POTS) is a chronic, debilitating condition that is characterized by an excessive increase in heart rate upon orthostatic challenge. Before the COVID-19 pandemic, POTS affected 0.5 % to 1 % of the U.S. population. Since the pandemic, the incidence has risen sharply, adding an estimated 6-7 million new cases in the U.S. Despite its importance, there is currently no reliable biomarker for POTS, leading to significant diagnostic delays. A major hurdle in identifying biomarkers is the heterogeneous nature of the syndrome. To address this, we focused on a homogeneous subgroup of post-COVID-19 POTS (PC-POTS) patients. We conducted quantitative proteomics on sera from 9 PC-POTS patients and 9 healthy controls, identifying 31 proteins with significantly different abundances in PC-POTS patients. Most elevated proteins were linked to actin filaments or immune functions/inflammation. Weighted Gene Co-Expression Network Analysis revealed module 7 (M7) correlated strongly with PC-POTS diagnosis and related traits. The key proteins in M7 included MTPN, TAGLN2, ADP-ribosylation factor 1, PDLIM1, PPIA, CNN2, LGALSL, TXN, TLN1, TUBA4A, IL4, TREML1, GP1BA, and, all highly correlated with these traits. Cell-type enrichment analysis revealed that M7 was highly associated with immune and neuronal cells. The main pathways identified in M7 included the integrin signaling pathway, blood coagulation, and glycolysis. These findings suggest that the key proteins in M7 could serve as biomarkers for PC-POTS. This study uses quantitative proteomics to identify potential biomarkers that differentiate PC-POTS patients from healthy controls, establishing a foundation for further research and validation.