In 1816, French physician René Laennec invented the stethoscope after recalling a simple childhood observation. He remembered watching children press their ears to long wooden beams to hear sounds from the other end. 

The idea returned to him when he was asked to examine a young woman with heart disease and felt it improper to place his ear directly against her chest.

Laennec rolled a sheet of paper into a narrow tube and placed one end on her chest and the other to his ear. The heartbeat sounded clear and amplified. He soon replaced the paper with a hollow wooden cylinder and called it a stethoscope, from the Greek words stēthos (chest) and skopein (to observe).

Published in his 1819 treatise De l’Auscultation Médiate, the invention transformed medicine by allowing doctors to “hear” the inner workings of the body for the first time.