Mediastinal lymphoma may infiltrate the conoarterial junction of the heart and cause life-threatening compression of the pulmonary artery. Partial debulking of the tumor along the left pulmonary artery and creation of a cavopulmonary anastomosis on the right pulmonary artery restored satisfactory perfusion of the lungs and unloading of the right ventricle in a 19-year-old woman. Remission of the tumor after chemotherapy allowed subsequent takedown of the cavopulmonary anastomosis.