Which Dutch physician is credited with inventing the first practical electrocardiograph?

The Dutch physician Willem Einthoven is credited with inventing the first practical electrocardiograph.

Einthoven transformed earlier observations of the heart’s electrical activity into a usable clinical instrument. Beginning in 1901, he developed the string galvanometer, which used a very thin conductive filament suspended between powerful electromagnets. Electrical signals from the heart moved the filament, and a beam of light recorded its motion as a tracing.

The original apparatus was enormous by modern standards. It weighed about 270 kilograms, required water-cooled electromagnets, and needed roughly five people to operate. Despite that bulk, it was sensitive enough to measure electrical activity through the body rather than requiring electrodes to be placed directly on the heart.

Einthoven also established terminology still used in ECG interpretation, including the P, Q, R, S, and T waveform labels and the concept of Einthoven’s triangle. He received the 1924 Nobel Prize in Physiology or Medicine for his work on the electrocardiogram.