Transradial coronary artery angiography (TRCAG) can have harmful effects on the radial artery as a conduit for coronary artery bypass graft surgery. The aim of this study was to evaluate the effects of trimetazidine (TMZ) on the functional recovery of the radial artery in patients who underwent TRCAG with flow-mediated dilation (FMD). Sixty patients, who underwent TRCAG using a 5Fr sheath were randomly assigned to the TMZ group or the control group. Baseline, post-TRCAG (<24 hours after TRCAG), and 10-week follow-up FMD were performed. In the control group of the cannulated arm, the baseline FMD was 11.4 +/- 3.5%, but the post-TRCAG FMD was significantly decreased to 4.2 +/- 2.9% (p <0.01). At 10-week follow-up, FMD was still decreased compared to baseline FMD (11.4 +/- 3.5% vs 5.9 +/- 3.3%, p <0.01). In the TMZ group of the cannulated arm, the difference in FMD between baseline and post-TRCAG was also significant (11.3 +/- 3.5% vs 6.3 +/- 4.0%, p <0.01). However, at 10-week follow-up, FMD was improved to 10.4 +/- 3.4%, and there was no difference in FMD between baseline and 10-week follow-up (11.3 +/- 3.5% vs 10.4 +/- 3.4%, p = 0.26). Repeated-measures analysis of variance confirmed the significance of the differences in FMD between the TMZ group and the control group (p <0.01). In conclusion, TMZ therapy after TRCAG reduced the endothelial dysfunction of the radial artery. This could contribute to positive effects for the radial artery conduit after coronary artery bypass graft surgery.