background: Heart failure is associated with degradation of cell functions and extracellular matrix proteins, but the trigger mechanisms are uncertain. Our recent evidence shows that active digestive enzymes can leak out of the small intestine into the systemic circulation and cause cell dysfunctions and organ failure. methods: Accordingly, we investigated in morning fasting plasma of heart failure (HF) patients the presence of pancreatic trypsin, a major enzyme responsible for digestion. results: Western analysis shows that trypsin in plasma is significantly elevated in HF compared to matched controls and their concentrations correlate with the cardiac dysfunction biomarker BNP and inflammatory biomarkers CRP and TNF-α. The plasma trypsin levels in HF are accompanied by elevated pancreatic lipase concentrations. The trypsin has a significantly elevated activity as determined by substrate cleavage. Mass spectrometry shows that the number of plasma proteins in the HF patients is similar to controls while the number of peptides was increased about 20% in HF patients. The peptides are derived from extracellular and intracellular protein sources and exhibit cleavage sites by trypsin as well as other degrading proteases (data are available ProteomeXchange with identifier PXD026332).ConnclusionsThese results provide the first evidence that active digestive enzymes leak into the systemic circulation and may participate in myocardial cell dysfunctions and tissue destruction in HF patients. conclusions: These results provide the first evidence that active digestive enzymes leak into the systemic circulation and may participate in myocardial cell dysfunctions and tissue destruction in HF patients. background: The online version contains supplementary material available at 10.1007/s12195-021-00693-w.