Electrocardiograph machine, c 1940.
© Science Museum / Science & Society Picture Library
Part of an electrocardiograph (ECG) machine supplied by the Physiology Laboratory, Leiden, Netherlands, and manufactured by the Cambridge Instrument Co, England. The 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. Willem Einthoven (1860-1927) developed the electrocardiograph during the early 1900s.