Accessory mitral valve tissue causing left ventricular outflow tract obstruction in D-transposition of the great arteries.

Two patients with D-transposition of the great arteries (D-TGA) were found to have an unusual form of left ventricular outflow tract obstruction. Both had ball-like accessory mitral valve tissue that partially occluded the outflow tract. In one patient there was an intact septum, while in the other there were ventricular septal defects. The appearances have been described previously, although not in D-TGA. Recognition of accessory mitral valve tissue may allow resection of the tissue at the time of repair of the transposition complex.