Objective: Coronary slow flow (CSF) is characterized by delayed opacification of coronary arteries in the absence epicardial occlusive disease. P wave duration and dispersion have been reported to be longer in patients with CSF. Nebivolol, besides its selective beta1-blocking activity, causes an endothelium dependent vasodilatation through nitric oxide release. In this study, we searched for the association between left ventricular diastolic functions and atrial conduction dispersion, the effects of nebivolol on P wave duration and dispersion in patients with CSF. Methods: This prospective case-controlled study included 30 patients having CSF and 30 subjects having normal coronary arteries in coronary angiography. The patients were evaluated with 12-leads electrocardiography and echocardiography before and three months after treatment with nebivolol. The difference between maximum and minimum P wave durations was defined as P-wave dispersion (PWD). Early diastolic flow (E), atrial contraction wave (A) and E deceleration time (DT) and isovolumetric relaxation time (IVRT) were measured. Unpaired and paired t-tests, Chi-square test, Mann-Whitney’s U-test and Pearson correlation analysis were used in statistical analysis. Results: Compared to control group maximum P wave duration (Pmax) (104.3±12.2 vs. 93.4±9.8 msec, p<0.001) and PWD (35.0±8.6 vs. 24.8±5.4 msec, p<0.001), DT (245.4±54.9 vs. 198.0±41.7 msec, p<0.001) and IVRT (112.9±20.8 vs. 89.5±18.2 msec, p<0.001) were significantly longer and E/A ratio (0.89±0.27 vs. 1.27±0.27, p<0.001) was lower in patients with CSF as compared with control subjects. There were no significant correlations of Pmax and PWD with clinical and echocardiographic variables. Systolic and diastolic blood pressures (130.5±15.5 mmHg to 117.8±12.3 mmHg and 84.5±9.8 mmHg to 75.0±6.2 mmHg, p<0.001), Pmax (to 98.7±11.7 msec, p=0.038), PWD (to 21.3±5.1 msec, p<0.001) and DT (to 217.3±41.4 msec, p<0.001) and IVRT (to 101.2±17.4 msec, p<0.001) significantly decreased and E/A ratio (to 1.1±0.23, p<0.001) significantly increased after treatment with nebivolol. Correlation analysis revealed that the change in PWD was not significantly correlated with any of the clinical and echocardiographic variables including decrease in blood pressures. Conclusions: Coronary slow flow is associated with prolonged P wave duration and dispersion and impaired diastolic filling. Nebivolol may be helpful in restoration of these findings. P wave duration and dispersion may not be associated with left ventricular function parameters in patients with CSF.