Invention of the Electrocardiograph

Willem Einthoven invented the string galvanometer in 1903, a device sensitive enough to record the heart's small electrical impulses from the body surface, and coined the letters P, Q, R, S and T still used to label the waves of an electrocardiogram trace. His string galvanometer replaced cruder earlier capillary electrometers and made accurate, repeatable electrocardiography clinically practical for the first time, revolutionizing the diagnosis of heart rhythm and conduction disorders. Einthoven received the 1924 Nobel Prize in Physiology or Medicine for the discovery of the mechanism of the electrocardiogram.