A 44-year-old man with HES who developed a large thrombus in the right ventricle as well as multiple occlusive coronary thrombi died of cardiac failure. Autopsy showed that a large thrombus in the right ventricle was associated with eosinophilic endocarditis. In addition, an occlusive thrombus formed in the circumflex and right coronary arteries with eosinophilic infiltrate in the walls. The findings suggest a causal relationship between coronary thrombosis and eosinophilia. To the authors' knowledge this is the first report to document the clinical and histological findings of coronary thrombosis in a patient with HES.