Background: It has been known that collateral flow may influence the long-term prognosis after percutaneous coronary intervention (PCI) because hemodynamic forces compete with the antegrade flow through the dilated lesion. The aim of this study was to assess collateral function and coronary hemodynamics of the total or nearly total occluded coronary lesions in acute and chronic coronary lesions by fractional flow reserve (FFR) using pressure wire. Methods: Between March 2011 and August 2011, 27 patients (24 men; mean age = 57.8짹12.1 year-old) who underwent PCI for total or nearly total occluded coronary lesions were included in this study. The FFR at maximum hyperemia induced by intravenous adenosine was determined at per- and post-intervention. The pressure-derived collateral flow index (CFI) was determined as (Pw - Pcvp)/(Pa - Pcvp), where Pw represents coronary wedge pressure, Pcvp central venous pressure, and Pa mean aortic blood pressure. Both were measured during transient coronary occlusion by a balloon inflation of 1 to 3 minutes. Results: Of these patients, chronic stable angina was present in 14 patients and acute coronary syndrome was present in 13 patients. Fifteen patients had a chronic total occlusion lesion (CTO) and 12 patients had an acute total occlusion (non-CTO). The mean pre-intervention FFR in CTO patient was 0.55 짹 0.12, whereas mean pre-intervention FFR in non-CTO patient was 0.69 짹 0.17. There was no significant differences between baseline CFI and recruitable CFI in patients with CTO (0.30 짹 0.11 versus 0.32 짹 0.11, p = 0.340) and non-CTO (0.19 짹 0.06 versus 0.22 짹 0.07, p = 0.170). There was a significant correlation between pre-intervention FFR and post-intervention FFR in CTO patients (r = 0.517, p = 0.048), whereas there was no significant correlation in non-CTO patients (r = 0.608, p = 0.062). Conclusions: The pre-intervention FFR in CTO patients are associated with post-intervention FFR. Collateral flow changes immediate after PCI was not observed both CTO and non-CTO patients.