The Authors describe two cases in which the outlet of the left ventricle was recreated by means of a bypass with a valve tube. The first is a case of correct levo-transposition of the great vessels with atresia of the pulmonary, in which a valve tube was applied between the inverted left ventricle and the right branch and trunk of the pulmonary. The second is a case of "long" fibrous subvalvular aortic stenosis, a relapse from former correction of membranous subaortic stenosis, in which bypass was applied between the left ventricle and the ascending aorta. This latter method, adopted by McGoon, is held by the Authors to be easier to apply and more physiological in its hemodynamic effects. The clinical and instrumental results were good in both cases. The hemodynamic and cardioangiographic controls carried out in the second case, 4 months after the surgical operation, showed the normal functioning of the prosthesis, an outflow equal to 60.3% of the total capacity through the bypass, and the ample neostomy of the left ventricle in systolic phase.