An unusual case of subaortic stenosis and aortic regurgitation caused by accessory mitral valve tissue in a 10 year old boy is reported. Two-dimensional and Doppler echocardiography revealed the characteristic feature of a mobile, parachute-like mass in the left ventricular outflow tract pro-lapsing into the aortic valve during systole and, thus, producing a systolic pressure gradient of 70 mm Hg between the left ventricle and aorta and causing mild aortic regurgitation. The accessory valve tissue was completely excised via an aortotomy without injury to the normal mitral and aortic valves. Two dimensional echocardiography provides excellent morphological information about the relationship between the accessory mitral valve tissue and the mitral and aortic valves, respectively. Accurate preoperative evaluation by two-dimensional echocardiography facilitates the successful surgical management of this rare condition.