We report an unusual case of cardiac sarcoidosis demonstrated by interventricular septal thickening. A 64-year-old woman was diagnosed with sarcoidosis involving the lungs, eyes, and skin. Three years later, renal dysfunction was detected during a periodic examination and a renal biopsy revealed non-caseating granulomas. Electrocardiogram results were normal, but an echocardiogram revealed thickening of the interventricular septum. Abnormal accumulation of gallium-67 and a perfusion defect in tecnetium-99-methoxyisobutylisonitrile scintigrams occurred in the interventricular septum. Magnetic resonance images showed T2-high intensity in the lesion. We considered the thickening to represent cardiac involvement of sarcoidosis. Oral prednisolone therapy diminished the interventricular septal thickening.