MMP9 and atrial fibrillation: Certainly, the plasma levels of several inflammatory biomarkers are elevated in patients with AF.8 This review article only focuses on the role of major biomarkers of inflammation—such as cluster of differentiation 40 ligand (CD40L), endothelin-1, fibrinogen, matrix metalloproteinase (MMP)-9, monocyte chemoattractant protein (MCP)-1, myeloperoxidase (MPO), plasminogen activator inhibitor (PAI)-1, and serum amyloid A (SAA)—in the progression and development of AF.