Leukemias are the most common childhood malignancy. It is a systemic disease presenting with different signs and symptoms. Extramedullary manifestations, in particular myeloid sarcoma (MS), are extremely rare, often challenging to identify, even more challenging to diagnose, and more than often misdiagnosed owing to its similarity with other solid tumors. We describe a previously healthy boy, aged 4 years, who had a cardiac mass lesion, presumed to be a MS, noted in the right atrium at the time of initial routine echocardiography. The lesion resolved without surgical intervention following the institution of multi-agent chemotherapy.