Lipoblastoma is a benign adipose tumor in children that has been described in various anatomic locations, most commonly the extremities. We describe the case of a 17-month-old boy diagnosed with cardiac lipoblastoma, a previously unreported primary cardiac tumor in children. Our patient presented with symptoms of coughing, wheezing, and hoarseness and was found to have a large mediastinal mass, which narrowed the left mainstem bronchus and compressed the right atrium and superior vena cava, causing superior vena cava syndrome. Surgical exploration revealed an intrapericardial soft tissue mass arising from the area of the posterior interatrial septum. Grossly, the resected mass was lobulated, pale yellow, and fatty with focal areas of gray myxoid tissue. Microscopically, the tumor consisted of both immature and mature adipocytes, with focal vascular myxoid areas containing lipoblasts, diagnostic of lipoblastoma. Two months after surgery, the patient was in good health without evidence of recurrence.