Laennec, Rene Theophile Hyacinthe, lay NEHK, ruh NAY tay aw FEEL ya SANT (1781-1826), a French physician and surgeon, invented the stethoscope in 1816. Doctors use this instrument to listen to the sounds of the heart and other organs. Laennec investigated diseases of the heart and the lungs, and published his conclusions in A Treatise on Mediate Auscultation in 1819. He died from tuberculosis, a disease on which he had become an expert. Laennec was born in Quimper, France. See also Stethoscope.