NPPB and heart failure: (Zhang et al. 2020) Of these studies, one prospective cohort study involving 2,490 patients with heart failure with reduced ejection fraction (HFrEF) or heart failure with preserved ejection fraction (HFpEF) found plasma TMAO levels to have a better predictive value than N-terminal pro-brain natriuretic peptide (NT-proBNP), an established risk marker in heart failure without direct connections to TMAO, for mortality and cardiovascular mortality in HFrEF patients.