Aim: The pathophysiology of cardiac syndrome X (CSX) has not been clearly identified, although multiple abnormalities including microvascular spasm, endothelial dysfunction, and atherothrombosis have been reported. It is known that eosinophils play an important role in vasoconstruction and thrombosis. We aimed to compare the eosinophil counts in patients with CSX versus controls. Materials and Methods This study included 50 patients with CSX (20 male, mean age 50.42 ± 9.6 years) and 30 control persons (10 male, mean age 49.16.11 ± 9.2 years). These participants underwent concurrent routine biochemical tests, and their eosinophil counts were obtained on whole blood count. These parameters were compared between groups. Results: Baseline characteristics of the study groups were comparable. Patients with CSX had a higher eosinophil count and mean platelet volume (MPV) value than the controls (339.4 ± 188 vs 132.7 ± 75 and 8.8 ± 0.2 vs 7.2 ± 0.1 fL; P < .001, respectively). Conclusion: As a result, our study revealed a relationship between eosinophil count and MPV in patients with CSX.