Intra-arterial aortoinfundibuloplasty is a newly developed aortic annular enlargement procedure in which, originally, the annulus was split anteriorly via the main pulmonary arteriotomy. An alternative method of aortoinfundibuloplasty was studied experimentally which creates spiral incisions on the free walls of both great arteries descending together into the aortopulmonary and infundibular septum via both commissures of right and left facing cusps of pulmonary and aortic valves. The valve prosthesis is implanted through this three-dimensional incision, followed by patch reconstruction. The ratio of annular augmentation was three sizes in two animals and four sizes in three animals. Immediate postoperative haemodynamics were satisfactory and there was no significant postoperative increase in systolic pressure gradient at the right ventricular outflow tract and in the right ventricular end-diastolic pressure. This alternative procedure could be applied to cases requiring radical annular enlargement and would give a wider view of both ventricular outflow tracts.