MMP9 and atrial fibrillation: Considerable evidence has been presented for a key role of MMP9 in ECM damage in multiple pathologies [28,29], including: rheumatoid arthritis [30]; some cancers (where MMP9 plays a role in angiogenesis, invasion, tissue remodeling and metastasis) [31,32]; vascular diseases, including brain ischemia [33]; cardiovascular syndromes, including atrial fibrillation [34], aortic aneurysms [35] and cardiovascular diseases including atherosclerosis [20,36,37,38].