Mean platelet volume (MPV) is an indicator of platelet activation, a central process in the pathophysiology of coronary heart disease (CAD). The importance of slow coronary flow (SCF) phenomenon results from its association with angina pectoris, acute myocardial infarction, hypertension and sudden cardiac death. The aim of this study is to evaluate the values of MPV in patients with SCF. MPV was measured in 84 consecutive patients with SCF and 88 patients with CAD and 84 control subjects. The association between thrombolysis in myocardial infarction (TIMI) frame count (TFC) and MPV level and other clinical and laboratory parameters were evaluated. There were no statistically significant differences in MPV between SCF group and CAD group. MPV was significantly higher in patients in the both SCF and CAD groups, compared with control group. The TFC for all the epicardial coronary arteries and the mean TFC were significantly higher in the SCF group than the both CAD group and control group. The mean TFC was positively and moderately correlated with MPV in the whole study population. To determine the independent predictors of mean TFC, a stepwise linear regression analysis was performed by including the parameters that were correlated with the mean TFC in the bivariate analysis. MPV level was the only independent predictor of the mean TFC (b = 0.312, p < 0.001). These findings have shown that MPV level is significantly associated with coronary blood flow and that elevated MPV level might be an independent predictor for the presence of SCF. We believe that further studies are needed to clarify the role of MPV in SCF complicated CAD, especially in relation to angiographic and clinical parameters, before we conclude that MPV to be used as a follow-up marker during the management of relevant patients.