Updated project metadata. Heart Failure with preserved ejection fraction (HFpEF) is a major health challenge affecting millions of people worldwide. Moreover, this disease presents multiple etiologies and associated comorbidities, leading to difficulties in diagnosis and limited therapeutic options. HFpEF underlying cellular pathophysiological mechanisms require further investigation. In this study, quantitative proteomic analysis by advanced mass spectrometry (SWATH-MS) was employed to investigate signaling pathways and mechanisms that correlate with HFpEF. Protein expression profiles were analyzed in HFpEF and non-HFpEF human left ventricular myocardium biopsy samples. Functional analysis revealed several proteins that correlated with HFpEF, including proteins associated with mitochondrial dysfunction, oxidative stress reaction, and inflammation. Additionally, proteomic profiles of HFpEF patients with diabetes mellitus indicate reduced mitochondrial oxidative phosphorylation and fatty acid oxidation capacity. Data obtained also reflects the known heterogeneity of HFpEF clinical variables. The proteomic characterization described in this work provides new insights and raises new questions related to HFpEF cellular pathophysiology, paving the way to additional studies focused on the development of novel therapies and diagnosis strategies for HFpEF patients.