From Hunter WG, Kelly JP, McGarrah RW 3rd, et al. Metabolomic profiling identifies novel circulating biomarkers of mitochondrial dysfunction differentially elevated in heart failure with preserved versus reduced ejection fraction: evidence for shared metabolic impairments in clinical heart failure. J. Am. Heart Assoc. 2016;5(8); with permission. Abbreviations: Ca++ indicates calcium; CMC, cardiomyocyte; COX, cyclooxygenase; IL, interleukin; IRS, insulin receptor substrate; K, potassium; MAPK, mitogen-associated protein kinase; TCA, tricarboxylic acid.