Heart measurement. Illustration of the first public demonstration of a heart measuring device, the electrocardiograph (ECG), by A.D. Waller at the Royal Society in 1887. Waller (1856-1922), a British physiologist, showed that the small voltages associated with heartbeat could be detected. With two of the dog's legs in bowls of salt water to improve the electrical contact, the voltages in its heart caused a deflection in the line on the mirror galvanometer (at lower left). Despite unfounded concerns amongst the audience that the dog would suffer an electric shock, the experiment was a success. The ECG was brought into clinical use by Willem Einthoven in 1903.