When accessory mitral valve tissue obstructs the left ventricular outflow tract resection is considered a sufficient and definitive procedure. We report the unusual case of a child who had undergone such resection at the age of 4 years and who developed, over a few years, a recurrent subvalvular aortic obstacle consisting, this time, in a fibromuscular tunnel. In a second operation performed at the age of 12, a septal patch was inserted to widen the subaortic channel which was approached through a trans-septal infundibular route. Control examination showed a satisfactory pressure gradient and a sinus rhythm.