We report a case of pulmonary trunk aneurysm extending into the left pulmonary artery, due to pulmonary hypertension secondary to mitral valve disease. The mitral valve was replaced with a bileaflet mechanical prosthesis. A Dacron graft interposed between main trunk and left pulmonary artery branch, and right pulmonary branch attached to the graft in an end-to-side fashion. Early postoperative angiogram revealed a very successful treatment.