A 60-year-old woman presented with a fever of unknown origin. Echocardiography revealed a large left atrial tumor protruding into the left ventricle during diastole. Laboratory investigation showed an elevated white blood cell count, C-reactive protein concentration, and interleukin-6 concentration. Magnetic resonance imaging showed hyperacute microinfarcts and multiple old lacunar infarcts. Surgery was performed under suspicion of cardiac myxoma. A dark red jelly-like tumor with an irregular surface was removed. Histopathological examination revealed cardiac myxoma, the surface of which was covered with fibrin and bacterial masses. Preoperative blood culture was positive for Streptococcus vestibularis. These findings were compatible with a diagnosis of infected cardiac myxoma. We used an antibiotic therapeutic regimen for infective endocarditis, and the patient was discharged home on postoperative day 31. Prompt diagnosis and treatment, including effective and efficient antibiotic therapy and complete tumor resection, increased the chance of a better outcome in patients with infected cardiac myxoma.