Objective: Cardiomyopathy (CMP) is a disorder associated with an increased risk of thromboembolism due to blood stasis, platelet activation and altered coagulation status. In this study, we aimed to investigate mean platelet volume (MPV) in patients with idiopathic CMP and ischemic CMP and to compare with those of the controls, and aimed to determine whether there is a relationship between MVP and echocardiographic parameters in patients with CMP. Methods: This study was designed as an observational cross-sectional study. A total of 100 subjects with idiopathic CMP (n=35), ischemic CMP (n=35) and controls (n=30) were included in the study. The MPV values were measured in all participants. All subjects underwent transthoracic echocardiography and angiographic evaluation. We used Chi-square test, one-way ANOVA and Pearson correlation tests for statistical analysis. Results: The MPV values were significantly higher in patients with idiopathic CMP and ischemic CMP than those of the controls (9.03±1.3 and 8.77±0.9 vs. 7.95±1.0 fl, respectively, p<0.001). The MPV values were although not statistically significant also tend to be higher in patients with idiopathic CMP than in patients with ischemic CMP (p=0.328). The MPV values were found to be positively correlated with left ventricular end-diastolic and end-systolic diameters (r=0.369, p<0.0001; r=0.325, p=0.001, respectively), and left atrial diameter (r=0.403, p<0.0001), but inversely correlated with left ventricular ejection fraction (r=-0.392, p<0.0001). Conclusion: Patients with idiopathic or ischemic CMP have higher MPV values indicating tendency to platelet aggregation regardless of the etiology, when compared to controls and an enlarged dysfunctional left ventricle may also be associated with higher MPV values.