Myeloperoxidase (MPO) is an enzyme found in myeloid cells, particularly in neutrophils, and to a lesser extent in monocytes and tissue macrophages. MPO plays an important role in the host defense against bacteria and viruses. Since MPO is also an important enzyme in the inflammatory process, and inflammation is a key component in the development and progression of atherosclerotic and other forms of cardiovascular disease, there is ongoing interest in the use of MPO as a biomarker in different fields of cardiology. We aimed to review the current state of literature regarding the role of MPO in cardiovascular disease, especially highlighting the practical implications of the fast growing data from clinical studies. © 2010 Future Medicine Ltd.