Hypereosinophilic syndrome is defined as persistent eosinophilia in the blood for more than 6 months, without any identifiable cause and with end-organ involvement evidence. Cardiac manifestations of HES include heart failure due to restrictive cardiomyopathy, arrhythmia, intraventricular thrombosis, and coronary artery involvement occurs frequently. In rare instances, coronary ectasia, aneurysms, or dissection can occur and cause morbidity and mortality in these patients.

A coronary aneurysm occurs rarely in adult patients with HES but to our knowledge, this is the first report of this association in a 14-year-old boy who was presented to us as coronary aneurysm due to hypereosinophilic syndrome.

Eosinophilic endomyocarditis is extremely rare in paediatrics. This case report aims to present the sequential changes from thrombotic to fibrotic stages of the cardiac involvement in a child with hypereosinophilic syndrome. Endomyocardial fibrosis progressively aggravated the severity of the mitral regurgitation. Bioprosthetic valve replacement was finally performed without recurrence of cardiac complications despite a late relapse of the underlying disease.

A boy with familial eosinophilia had the hypereosinophilic syndrome, with involvement of mitral and tricuspid valves. Between the ages of 11 and 20 years, he underwent eight surgical procedures on his atrioventricular valves. The pathology included recurrent thrombotic vegetative masses related to hypereosinophilia. Initial repair of the mitral valve was shortlived, but recurrent repairs of the tricuspid valve were helpful. Mechanical prostheses inserted in the mitral position thrombosed despite anticoagulant therapy, and bioprosthetic valves deteriorated with thrombus, fibrosis, or tearing. The hypereosinophilic syndrome is unusual in children, and produces additional problems with valvar surgery.