To systematically explore the low molecular peptidome, we conducted a cross-sectional mass spectrometry analysis from 486 patients with HF and 98 age-matched non-HF controls. We quantified 21 694 unique peptides in plasma, which were ranked according to (1) the relative upregulation in HF versus controls, (2) pattern similarity to bioactive peptides by an adapted machine learning method, and (3) association with clinical outcome.