Copyright © 2022 Burhan Aslan et al.Background: The coronary slow flow phenomenon (CSFP) is an atherosclerotic process that causes ischemia at the microvascular level. The CSFP may affect P wave durations, especially P wave peak time (PWPT), by microvascular ischemia, left ventricular diastolic dysfunction, and changes in the left atrial dimension. Therefore, in the present study, we aimed to assess PWPT in the CSFP. Method: One hundred and ninety-five patients were included in this single-center, retrospective study. Ninety patients were enrolled in the CSFP group and 105 patients in the control group. PWPT was defined as the duration between the beginning and peak of the p wave and obtained from the leads Dıı and Vı. Results: The mean age of the study population was 48.5 ± 9.5, and 108 (55.3%) of the patients were female. We found PWPT was longer in the CSFP group than in the control group. Correlation analysis showed a positive correlation between PWPT in both leads (DII, Vı) and left atrial anterior-posterior diameter, mean TIMI frame count (TFC), and E/e. A significant relationship was observed between mean TFC, E/e, EF, heart rate, and PWPT in lead Dıı (β coefficient = 0.33, 95% CI 0.44-1.33, p < 0.001, β coefficient = 0.23, 95% CI 0.25-1.85, p=0.01, β coefficient = -0.140, 95% CI -1.04--0.53, p=0.03, and β coefficient = -0.13, 95% CI -0.29--0.014, p=0.03, respectively) in multivariable linear analysis. Conclusion: In the present study, we found prolonged PWPT in patients with the CSFP and found a relationship between PWPT and mean TFC.