HEART TRANSPLANT SURGEONS Scarce pair of Mayo Brothers first day postal covers bearing their stamp, Rochester, Minn., Sep. 11, 1964, each signed by ten surgeons who undertook heart transplant operations, including doctors: LOWER, LILLEHEI, FLEMMIA, JOHNSON, COOLEY, KANTROWITZ, SZENTETARY, DE BAKEY, KAHN and LEPLEY. Very good, two pieces.