Patients experience moderate to high level of anxiety before cardiac catheterization. This study aimed to investigate the effect of voice of Quran on anxiety before cardiac catheterization. Methods: in this randomized controlled trial, 60 patients who met the inclusion criteria were conveniently sampled and randomly allocated to the experimental and control groups. In the experimental group, patients received 18 minutes of voice of Quran, whereas in the control group, patients had 18 minutes of rest in bed. The level of anxiety was measured immediately before, and immediately after the study using the state trait anxiety inventory (stai). Results: before the study, there was no significant difference between the study groups in terms of the mean score of state and trait anxiety as well as the mean scores of total stai. However, after the study, the mean scores of state and trait anxiety as well as the mean scores of total stai in the experimental group were significantly lower than those of the control group. Conclusion: the findings of the study demonstrated that the voice of Quran can significantly improve patients’ anxiety before cardiac catheterization.