It is known that increased frontal QRS-T angle, which is a new ventricular repolarization marker is associated with adverse cardiac outcomes. It has been observed that the coronary slow-flow (CSF) phenomenon can cause arrhythmias and sudden cardiac death. The aim of our study is to investigate the relationship between CSF in patients and the frontal QRS-T angle. A total of 200 patients, 97 of who had CSF and 103 with the normal coronary flow (NCF), were included in our study. The CSF group was divided into two groups; single-vessel CSF and multi-vessel CSF. The TIMI-frame count was calculated from the coronary angiography images of each patient. 12-lead electrocardiography (ECG) records were examined. The frontal QRS-T angle was obtained from the automated reports of the ECG device. The mean age of the study population was 50.7 ± 9.5 and 102 (51%) of patients were female. The frontal QRS-T angle was significantly higher in patients with CSF compared to the NCF group [48(31-64) vs 37(25-46), p = 0.001]. A positive correlation was observed between the frontal QRS-T angle and TIMI-frame count in the correlation analysis performed separately for LAD, Cx, RCA patients with CSF (respectively; r = 0.340 and p < 0.001, r = 0.262 and p = 0.002, r = 0.247 and p = 0.003). The frontal QRS-T angle was higher in patients with multi-vessel CSF than in patients with single-vessel CSF [53.5(41.5-76.5) vs 43.0(23.5-60.5), p = 0.039]. There is a positive correlation between frontal QRS-T angle and TIMI-frame count. The frontal QRS-T angle is higher in patients with CSF. Also, frontal QRS-T angle was higher in the multi-vessel CSF group.