Who invented the modern clinical electrocardiogram?

Willem Einthoven invented the modern clinical electrocardiogram.

Einthoven, a Dutch physiologist, developed the string galvanometer in the early twentieth century and used it to record the heart's electrical activity with unprecedented accuracy. His instrument was far more sensitive than earlier devices and produced recognizable waveforms that could be compared between patients.

He introduced the labels P, Q, R, S, and T for the principal waves of the cardiac tracing. These labels remain standard in electrocardiography, although the exact electrical events represented by the waves are now explained using modern cardiac physiology.

The electrocardiogram, or ECG, is non-invasive and can help identify abnormal rhythms, heart attacks, conduction problems, and other conditions. Einthoven received the 1924 Nobel Prize in Physiology or Medicine for his discovery of the mechanism of the electrocardiogram.