CRP and atrial fibrillation: Of the measured plasma proteins (IL-6, MMP-9, C3a, and C5a), positive significant correlations were found only between C5a and C3a (r = 0.376, P < 0.001) and between C5a and MMP-9 (r = 0.166, P = 0.029), and only the plasma IL-6 level was significantly correlated with serum CRP level (r = 0.494, P < 0.001) and AF IL-6 level (r = 0.289, P < 0.001).