Electrocardiograph in use, 1927.
© Science Museum / Science & Society Picture Library
Plate from 'The Cambridge Instrument Company', catalogue of medical equipment. The electrocardiograph (ECG) detects and records the tiny electrical signals that coordinate the heart's beats, as these 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 ECG during the 1900s.