Accessory atrioventricular valvar tissue is uncommon and, on occasion, has been identified as a cause of ventricular outflow obstruction. Accessory tricuspid valvar tissue has been reported to cause subpulmonary obstruction but infrequently has accessory tissue arising from the mitral valve been associated with obstruction. This paper reports two cases of subvalvar obstruction; the first in association with a ventricular septal defect causing subaortic obstruction and the other in association with congenitally corrected transposition and a ventricular septal defect, causing subpulmonary obstruction.