New biomarker in heart failure with reduced ejection fraction.

eart failure is a serious condition because of the structural and/or functional cardiac disorders,1–3 in which not only heart failure with preserved ejection fraction (HFpEF) but also heart failure with reduced ejection fraction (HFrEF) are substantially involved.4,5 Because of the poor prognosis of patients, especially those with HFrEF,6 various therapeutic options have been developed during the past 3 decades, such as β-blockers, angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARB), implanted devices such as cardioverter-defibrillators (CRT-D) or implanted cardioverter-defibrillators (ICD), and left ventricular assist devices.7 To monitor the severity of heart failure, we usually examine blood levels of brain natriuretic peptide (BNP) or N-terminal pro-BNP (NT-proBNP); however, a more sensitive monitoring system is sometimes required in the clinical setting. H