BACKGROUND Isolated mitral valve aneurysm is rarely reported in children. In most cases it is associated with an underlying disease such as infective endocarditis. MVA can lead to severe complications that needs surgical intervention. METHODS In this report, we present a 9-year old asymptomatic male patient with anterior mitral valve aneurysm and rhythm disturbance diagnosed incidentally during pre-operative evaluation. CONCLUSIONS Being rare in children, isolated MVA should be kept in mind in the differential diagnosis of mass lesions seen on the atrial side of the mitral valve. A 24-hour electrocardiogram may define subtle rhythm disturbances in these patients.