The rapid, accurate determination of the electrical axis of a patient's heart is very useful for diagnosis. This determination can be made readily by using six electrocardiographic leads. The procedure for interpreting the data from these leads and determining the electrical axis of. the heart is charted. This method uses key leads I and a VF to determine the quadrant where the axis is located and secondary leads II, III, a VR, and a VL to find the axial position within the quadrant. When either I or a VF is isoelectric, only one key lead is used.