NPPB and heart failure: To address this hypothesis, we investigated the relationship between CMD-related ischemia measured by coronary flow reserve (CFR) and N-terminal pro-B-type natriuretic peptide (NT-proBNP), an established biomarker of clinical heart failure [7–11], which is synthesized and secreted by ventricular cardiomyocytes under periods of increased myocardial wall stress and is also expressed in response to ischemia [12,13].