Patients with myxoma normally present with cardiovascular symptoms due to mitral valve obstruction caused by the tumor. However, some cases are difficult to diagnose because the findings of auscultation are normal and there are no cardiovascular symptoms. A 62-year-old man presented at a nearby clinic with a fever. No cardiac murmurs were heard on a physical examination. Abdominal ultrasonography was conducted to evaluate the origin of the fever, and a giant left atrial myxoma was discovered incidentally. Although many myxoma cases are found on transthoracic echocardiography, we herein describe a case of a giant left atrial myxoma incidentally discovered on abdominal ultrasonography.