The scene is familiar to anyone who has seen a TV medical drama. The old man on the gurney goes into cardiac arrest, his heart monitor emitting an urgent whine. A doctor grabs a paddle in each hand, barks a warning – Clear! – and applies a jolt of electricity to the patient’s bare chest. The body thrashes violently, but a tense moment later, the monitor resumes its steady beeping.

That this procedure is instantly recognizable to people who’ve never set foot in an emergency room is largely due to Boston physician Bernard Lown, inventor of the modern defibrillator. It wasn’t always clear that passing current through a patient’s body could restore a wayward heart. In 1775, a Danish veterinarian used electricity to stun and revive a chicken. It wasn’t until 1955, though, that physician Paul Zoll resuscitated a human patient by applying a burst of alternating current to his chest. AC defibrillation didn’t have a high success rate, but since its recipients were nearly dead anyway, its drawbacks did not receive much scrutiny.

That began to change in 1959, when 37-year-old Lown faced a desperate situation. A patient arrived at the emergency room with short breath and a rapid pulse. When the customary drugs failed to slow the man’s racing heart, Lown recalled Zoll’s work. Although defibrillation had never been attempted in this type of case, Lown obtained permission from the man’s wife and delivered a shock to his chest. To Lown’s relief, the treatment worked. But three weeks later, when the man returned with the same problem, Lown’s attempt to shock the heart back to normal made the muscle contract erratically instead. Doctors opened the man’s chest to apply electrodes directly to the heart. The patient survived the night but died soon after.

Lown spent a year trying to find out what had gone wrong. He finally realized that the alternating current doctors were using did enormous damage to the heart muscle. Lown enlisted engineer Baruch Berkowitz to help find a safer, more effective treatment. The two developed a defibrillator based on direct current, which delivers a single pulse of electricity instead of a current that repeatedly switches direction. Within a few years, this new machine had replaced its AC predecessor in hospitals, and it has been saving lives – on TV and in real life – since.