Aim To investigate the effect of exercise load test on QT dispersion in patients with coronary slow flow (CSF). Methods 81 cases of CSF patients with chest pain underwent coronary angiography, without coronary artery obvious stenosis (stenosis of the lumen diameter＜40%) were selected as the slow blood flow group. 80 cases with normal coronary angiography and exercise load test electrocardiogram negative were selected as the control group. Maximum corrected QT interval (QTc_max), minimum corrected QT interval (QTc_min) and corrected QT dispersion (QTcd) were calculated for each case before and after exercise. Results At rest time, QTc_max in the slow blood flow group was significantly longer than that in the control group (P＜0.05), the QTcd of the slow blood flow group increased significantly compared with the control group (P＜0.05), but there was no significant difference in QTc_min between the two groups. After exercise, the QTc_max and QTc_min in the slow blood flow group were significantly longer than those in the control group (P＜0.05), and QTcd significantly increased compared with the control group (P＜0.05). In the slow blood flow group, only 9 cases of exercise load test were positive, accounting for 11.11%. After exercise, the QTcd was significantly decreased compared with rest in the slow blood flow group (46.41±12.21 ms vs 62.81±17.18 ms, P＜0.05). In the control group, there was no significant change of QTcd before and after exercise. Conclusion QTcd in CSF patients is higher than that in normal person, and the exercise will make it significantly reduced.