This report describes a 1½-year-old boy who succumbed to acute obstruction of the left ventricular outflow tract by a cardiac rhabdomyoma. He was admitted to have a transient loss of consciousness episode evaluated. A mobile intracardiac mass obstructing the left ventricular outflow tract and protruding into the aortic root during systole was detected by transthoracic echocardiography. At autopsy, it was confirmed to be a rhabdomyoma.