Wikipedia:Imperial College/Project Page/Sandbox intro

The electric axis of the heart is the net direction in which the wave of depolarisation travels. It is measured using an electrocardiogram (ECG). Normally, this begins at the atrioventricular node (AV node); from here the wave of depolarisation travels down to the apex of the heart. The hexaxial reference system can be used to visualise the directions in which the depolarisation wave may travel. On a hexaxial diagram (see figure 1):
 * If the electrical axis falls between the values of -30° to +90° this is considered normal.
 * If the electrical axis is between -30° to -90° this is considered left axis deviation.
 * If the electrical axis is between +90° to +180° this is considered right axis deviation.