Two different monomorphic VTs were observed in two patients after a corrective operation for tetralogy of Fallot. The activation pattern of the wavefronts of the two VTs were different: in a counter-clockwise direction around the anatomical obstacle due to a ventriculotomy of the right ventricle in one VT; and in a clockwise direction around the same obstacle in the other VT. The different revolutions of the wavefronts could be the mechanism for the different morphologies of VT.