Einthoven's triangle

Einthoven's triangle is an imaginary formation of three limb leads in a triangle used in the electrocardiography, formed by the two shoulders and the pubis. The shape forms an inverted equilateral triangle with the heart at the center. It is named after Willem Einthoven, who theorized its existence.

Einthoven used these measuring points, by immersing the hands and feet in pails of salt water, as the contacts for his string galvanometer, the first practical ECG machine.