Working on the heart had long been considered too dangerous. In fact, in the last decade of the 19th century, famed Austrian surgeon Theodor Billroth declared: "Any surgeon who would attempt an operation of the heart should lose the respect of his colleagues." Even though doctors knew from electrocardiograph readings and other evidence that a heart might be malfunctioning or have anatomical defects, it was practically impossible to do anything about it while the heart was still beating. And stopping it seemed out of the question because blood had to circulate through the body continuously to keep tissues alive. In the first decades of the 20th century, surgeons performed some cardiac procedures on beating hearts, but with limited success.

Then in 1931, while caring for a patient with blood clots that were interfering with blood circulation to her lungs, a young surgeon named John Gibbon had a bold thought: What if oxygen-poor blood was pumped through an apparatus outside the body that would oxygenate it, and then was pumped back into the body? He began working on the problem, despite the skepticism of his fellow doctors. Teaming with his wife, laboratory technician Mary Hopkins, Gibbon fashioned a rudimentary heart-lung machine from a secondhand air pump, glass tubes, and a rotating drum that exposed blood to air and allowed it to pick up oxygen. Perfecting the device took more than two decades and countless experiments on animals. Then in 1953 Gibbon performed the first-ever successful procedure on a human using a heart-lung pump to maintain the patient's circulation while a hole in her heart was surgically closed. The era of open-heart surgery (so called because the chest cavity was opened up and the heart exposed) was born, and in the next decades surgeons would rely on what was simply called "the pump" to repair damaged hearts, replace defective heart valves with bioengineered substitutes, and perform thousands and thousands of life-extending coronary artery bypass operations to curb heart attacks.

The development of the pacemaker involved similar moments of insight and the nuts-and-bolts efforts of inspired individuals. For Wilson Greatbatch, an electronics wizard with an interest in medicine, the light flashed on in 1951 when he heard a discussion about a cardiac ailment called heart block, a flaw in the electrical signals regulating the basic heartbeat. "When they described it, I knew I could fix it," Greatbatch later recalled. Over the next few years he continued trying to create a device that could supply a regular signal for the heart. Then, while working on a device for recording heart sounds, he accidentally plugged the wrong resistor into a circuit, which began pulsing in a pattern he instantly recognized: the natural beat of a human heart.