Heart failure is associated with degradation of cell functions and extracellular matrix proteins, but the trigger mechanisms are uncertain. Our recent evidence in acute multiorgan failure suggests that active digestive enzymes leak out of the small intestine into the systemic circulation and cause cell dysfunctions and organ failure. Accordingly, we investigated in morning fasting plasma of heart failure (HF) patients the presence of pancreatic trypsin, a major enzyme responsible for digestion. Western analysis shows that trypsin in plasma is significantly elevated in HF compared to matched controls and their concentrations correlate with inflammatory biomarkers. 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 proteins in the HF group is similar to controls while the number of peptides was increased about 20% in the HF patients. The peptides are derived from extracellular and intracellular protein sources and exhibit cleavage sites by trypsin as well as other degrading proteases. These results provide first evidence that active digestive enzymes leak into the systemic circulation and may participate in myocardial cell dysfunctions and tissue destruction in HF.