Yet, most studies were done in selected populations (e.g., patients with heart failure [10,15,17,20,21], atrial fibrillation [13,18] or primary aldosteronism [12,14]), reported on a single MMP (i.e., MMP-2 [15,20,21], MMP-9 [13,18] and TIMP-1 [19]) and did not adjust for potential confounders [10,11,13,16,17,18,21]. This evidence concerns the gene MMP9 and heart failure.