Background:The endothelium of the vascular tissue plays an important role in regulating vascular homeostasis. In addition, patients with cardiac syndrome X have altered endothelial functions resulted in endothelial dysfunction. We designed a study, evaluated the quantification of coronary blood flow in patients with cardiac syndrome X by using the TIMI frame count method.Methods and Results:In our study, 41 patients with cardiac syndrome X and 45 control subjects were studied. All patients underwent selective coronary angiography. The measurement of coronary blood flow was assessed by means of TIMI frame count method. TIMI frame counts for each major epicardial coronary artery were significantly higher in cardiac syndrome X group compared to the control group (for LAD: 37 ±19 vs. 23 ± 7, respectively, P<.001; for LCx: 26 ± 13 vs. 19 ± 6, respectively, P=.001; for RCA: 22 ± 10 vs. 16 ± 7, respectively, P=.004). In addition, no significant correlation was found between TIMI frame counts and baseline characteristics.Conclusion:We have demonstrated that patients with cardiac syndrome X have higher TIMI frame counts and so decreased coronary blood flow for each major epicardial coronary artery compared to control subjects, indicating endothelial dysfunction/microvascular angina.