Nine electrocardiogram traces (ECGs), 1887-1903

UNITED KINGDOM - MARCH 15: Photographs taken by physiologist Augustus Waller, some possibly on open hearts, during the cardiology research he carried out at St Mary's Medical School, London, between 1884 and 1903. In 1887, Waller published the first human electrocardiogram. It was recorded by Thomas Goswell, a technician at the laboratory. The Dutch physiologist Willem Einthoven (1860-1927) built on Waller�s work and developed the electrocardiograph during the 1900s. An electrocardiograph detects and records the tiny electrical signals that coordinate the heart's beats, and which can indicate heart disorders. The signals ripple outwards and are picked up by metal sensors stuck to the skin. (Photo by SSPL/Getty Images)