In the 1950s, engineer Wilson Greatbatch was building a device to record heartbeats when he accidentally inserted the wrong resistor. Instead of recording, the circuit produced a steady pulse—exactly the kind needed to regulate a heartbeat.

Realizing its potential, Greatbatch developed the first implantable pacemaker. In 1960, it was successfully used in a patient who lived two more years—a major breakthrough.

He later improved the device with long-lasting lithium batteries, making pacemakers more reliable. Today, millions rely on this life-saving invention born from a simple mistake.