Cardiac defibrillators have come a long way in the last half a century. If you pay enough attention, you will notice that defibrillators are ubiquitous: now readily seen hanging on public institution walls like first aid kits of old. IEEE Spectrum magazine has an extensive article covering the history of the defibrillator, including the pictured device invented by Dr. Claude Beck in the 1940′s at University Hospitals of Cleveland. Regulating the electric current to stimulate the heart is an interesting science from both the clinical as well as the engineering perspective, and Spectrum gives a rather in depth overview of the functionality of modern fully automatic units by tracing the device’s development through the years.
A snippet:

Kouwenhoven and Knickerbocker’s observation was picked up by a pioneering cardiac surgeon, Claude Beck, at the University Hospitals of Cleveland. He began delivering ac directly to the exposed hearts of animals he had put into ventricular fibrillation. Beck might have continued methodically with his animal experiments, except that in 1947 a 14-year-old patient’s heart stopped during surgery. Out of desperation, Beck ordered that his research unit be brought up from the hospital’s basement. This simple defibrillator consisted of a transformer to isolate the patient from the 110-volt ac wall supply, a variable resistor to limit the current to a heart-safe value, and two metal tablespoons with wooden handles to deliver the jolt to the exposed heart [see “Saved by a Spoon”].
The first shock failed, so Beck administered a second. That brought the patient back to life, and the event made national news. But because so little was known about why the technique worked or how to improve it, these crude ac systems persisted for several years. Recipients of closed-chest ac defibrillation tended to suffer unpleasant side effects from the large steady currents, including broken ribs and damage to the heart ­muscle—if they were saved at all.
Unknown to Beck and his colleagues in America, investigators in Europe and Russia were far ahead of them in animal research and were beginning to use a single pulse, or dc, defibrillation. In the 1890s, Jean-Louis Prévost and Frederic Batelli, two physiologists at the University of Geneva, revived animals with a capacitor discharge delivered directly to the heart.
Decades later, one of their graduate students, Lina Schtern, moved to the Soviet Union and continued to refine the ­technique—that is, until she received a death sentence during a crackdown on intellectuals under Joseph Stalin. She was eventually pardoned by the dictator himself, who (according to accepted rumor) believed that she could bring people back from the dead.

Read the whole thing at IEEE Spectrum…