This report describes the diagnosis and surgical treatment of a 48 year old patient with congenital right pulmonary arterial ostial stenosis, no intra- or extracardiac shunts and systemic levels of pressure in the main and left pulmonary artery with pulmonary vascular obstruction in the left lung. Operation consisted of a bypass graft of 10 mm woven Dacron from the main pulmonary artery to the distal right pulmonary artery producing an immediate 50 percent reduction in mean left pulmonary arterial pressure. Late postoperative evaluation revealed equal perfusion of both lungs, maintenance of the reduced pulmonary arterial pressure and improvement from New York Heart Association functional class IV to class I.