F2R and atrial fibrillation: An immunohistological analysis of the LA from patients with AF showed strong thrombin expression in the myocardium and thick, fibrotic subendocardial space of the LA (averaged scores: 3.0 in the endocardium/subendocardium, 3.5 in the myocardium) (Figure 4) as well as strong prothrombin expression (averaged scores: 3.5 in the endocardium/subendocardium and 4 in the myocardium) and PAR-1 expression (averaged scores: 3.5 in the endocardium/subendocardium and 2.5 in the myocardium) (Figure 4).