Background: When there is minimal epicardial coronary stenosis, the coronary slow flow phenomenon (CSFP) is characterized by delayed distal artery opacification. The sluggish velocity of dye in coronary arteries is known as the slow coronary flow (SCF) phenomenon. Dispersion in QT interval and P wave are 2 electrocardiographic findings which can predict predisposing of individuals for developing fatal arrhythmia. The aim of this study was to find association between QT interval and P wave dispersion in acute coronary syndrome patients with CSFP. Patients and methods: This cross-sectional study was carried out on 200 cases undergoing diagnostic coronary angiography; Group 1 included 100 patients with acute coronary syndrome and CSFP, and Group 2 included 100 patients with acute coronary syndrome without CSFP. Results: We found no statistically significant differences between Group 1 and Group 2 according to demographic data, diabetes mellitus, hypertension, dyslipidemia and smoking. QTD, PWD, CTFC LAD, CTFC LCX, CTFC RCA and CTFC were significantly higher among Group 1. QTD showed AUC of 0.996. At best cutoff value of 46.5, sensitivity was 99.75% and specificity was 99.8%. PWD showed AUC of 0.99. At best cutoff value of 23.5, sensitivity was 96.55% and specificity was 98.3%.QT interval showed significant positive correlations with PWD and CTFC. Otherwise, QT interval showed non-significant correlations with other parameters in all studied cases. Conclusion: There is an association between QT interval and PWD in acute coronary syndrome patients with slow coronary flow phenomenon.