This electrocardiogram shows limb lead reversal. The characteristic features demonstrated here include an inverted P wave in lead I in combination with negative QRS and T waves in the same lead. This identifies either dextrocardia or limb lead reversal. The normal precordial leads V1-V6 rule out dextrocardia. With arm lead reversal, aVR is aVL and viceversa. This is one of the commonest technical errors and mimics right axis deviation.