Today’s Doodle celebrates the birth of Willem Einthoven, the Nobel Prize-winning Dutch physiologist who pioneered electrocardiography—a quick, painless, and effective method of studying the rhythms of the heart and diagnosing cardiovascular disease.

Born on the island of Java (now Indonesia) on this day in 1860, Einthoven grew up aspiring to follow in the footsteps of his father who had been both a doctor and military medical officer. By 1886 he had become a professor of physiology at the University of Leiden, focusing on optics, respiration, and the heart.

In 1889, Einthoven attended the First International Congress of Physiologists, where he watched a demonstration of a device known as the “Lippmann capillary electrometer” recording the electrical activity of the human heart. After analyzing the results, Einthoven recognized the need for a more accurate device, and began work on his string galvanometer, based on the technology used to amplify signals along underwater cables.

Balancing a fine string of quartz coated in silver between the two poles of a magnet, Einthoven’s invention precisely measured variations in electrical current. In 1901 he announced the first version of the string galvanometer, and soon published the world’s first electrocardiogram or ECG, a printed record of a human heartbeat. Einthoven studied the ECG patterns, identifying five “deflections” of normal heart function, learning how to interpret deviations that signal circulatory problems and heart disease.

Einthoven’s groundbreaking research won him the 1924 Nobel Prize for Physiology or Medicine. Today, ECG machines are still used in hospitals all over the world, and while the technology has evolved greatly, they still work according to the same basic principles and techniques developed by Einthoven, who is now remembered as the father of modern electrocardiography.