Einthoven’s triangle [Willem Einthoven] , an equilateral triangle whose vertices lie at the left and right shoulders and the pubic region and whose center corresponds to the vector sum of all electric activity occurring in the heart at any given moment, allowing for the determination of the electrical axis. Einthoven’s triangle is approximated by the triangle formed by the axes of the bipolar electrocardiographic (ECG) limb leads I, II, and III. The center of the triangle offers a reference point for the unipolar ECG leads.
