The presence of a pathologic mass in the right ventricle (RV) may lead to hemodynamic consequences and to a life-threatening incident of pulmonary embolism. The diagnosis of an unstable thrombus in the right heart chamber usually necessitates intensive treatment to dissolve or remove the pathology. We present a report of an unusual complication of severe ketoacidosis: thrombus in the right ventricle, removed from the tricuspid valve (TV) apparatus. A four-year-old boy was diagnosed with diabetes mellitus (DM) type I de novo. During hospitalization, a 13.9 × 8.4 mm tumor in the RV was found in a routine cardiac ultrasound. The patient was referred for surgical removal of the floating lesion from the RV. The procedure was performed via midline sternotomy with extracorporeal circulation (ECC) and mild hypothermia. Control echocardiography showed complete tumor excision with normal atrioventricular valves and heart function. Surgical removal of the thrombus from the tricuspid valve apparatus was effective, safe, and a definitive therapy for thromboembolic complication of pediatric severe ketoacidosis.