Procalcitonin (PCT) is a peptide precursor of the hormone calcitonin and is a marker of inflammation in bacterial infections and heart failure. Severe or worsening heart failure is associated with systematic inflammation, and patients with heart failure have significantly higher plasma PCT concentrations than healthy subjects. High PCT levels are associated with worse outcomes, and quantitative measurements of PCT offer a prognostic value that correlates with clinical outcomes and can potentially guide drug therapy.