Acute lymphoblastic leukemia (ALL) is a systemic disease that is presented with different symptoms and signs. Cardiac manifestation is rare in ALL, but it is very important and needs appropriate management. It usually presents as leukemic myocardial infiltration and in the presence of cardiac mass comprehensive evaluation for other etiologies is mandatory. We reported on a 6-year-old boy in remission phase of ALL and large cardiac mass in the right atrium with obscure early symptoms and signs, in whom infective endocarditis (IE) was diagnosed and appropriate medical treatment was performed. Because the mass was sustained, surgical resection was considered for the patient.