A case of congenital rhabdomyoma of the heart in a 5-month-old Korean infant is described. The patient presented with a congenital supraventricular tachyarrhymia that was detected in utero by fetal sonography. The tumor was multiple, but no obvious association with tuberous sclerosis complex was demonstrated. Microscopic examination revealed classic "spider cells" with rich glycogen content. Ultrastructurally, the cells contained numerous leptofibrils, clumped Z band material, and desmosome-like cell junctions. The case is a second documented case of cardiac rhabdomyoma in this country, and its presentation as an etiological factor of supraventricular tachycardia is a very unusual manifestation.