The electrical activity of the heart starts in the ‘internal pacemaker’, which is called the sinoatrial node. sinoatrial node. -Right atrium Normal rythm - Sinus rythm

Changes to the normal flow of electricity through the heart can be shown on an ECG and may indicate damaged heart muscle.

Each view of the heart is described as a ‘lead’. The word ‘lead’ does not refer to the electrodes.

The rhythm of the heart can be determined from only one view, i.e. one lead (this requires two electrodes). Leads: I, II, III, VL, VF and VR

Six electrodes are attached to the chest, recording leads V1 to V6 . Accurate placement of these electrodes is essential for comparing later ECGs

RRedRight arm
GGreenLeft Leg
BBlackRight Leg
YYellowLeft Arm

; the voltage calibration should be set so that 1 mV causes 1 cm of upwards deflection