The exact pathophysiology of slow coronary flow (SCF) phenomenon, characterized by delayed opacification of coronary arteries during coronary angiography, is still unknown, although endothelial dysfunction, inflammation, vasomotor disorders and atherosclerosis are shown. The present study was conducted to investigate whether there is a coagulation pathway abnormality in patients with SCF measuring plasma factor XI and XII activity. The study included 55 patients with angiographically proven SCF (group I) and 40 individuals with normal coronary flow (NCF, group II). Baseline demographic properties were similar in both groups. Echocardiographic parameters were also similar in patients with SCF and NCF. Factor XI activity was significantly higher in group I when compared with group II. Factor XII activity was also significantly higher in group I when compared with group II (108.9 ± 19 vs. 98.8 ± 20, P = 0.018 and 131.2 ± 17 vs. 119.1 ± 16, P = 0.001, respectively). We conclude that SCF phenomenon appears to be associated with enhanced procoagulant state, which may support the role of inflammation and atherosclerosis in the pathogenesis of this phenomenon.