Defibrillation electrodes should be placed on the bare chest with the electrode marked as sternum usually in the right infraclavicular region and the electrode marked as apex in the inferolateral left chest, lateral to the left breast. Alternate positioning on the lateral sides of the chest or biaxillary position can also be used. Another method is to keep the left pad in the standard apical position and the right pad on the right or left upper back. If a pacemaker or other implanted medical device is present, the pad should be kept a minimum of 2.5 cm from the device. Antero-posterior shocks should be considered to minimise the damage to implanted devices whenever feasible. In case an implanted cardioverter device is delivering a shock, as evidenced by muscle contractions similar to that seen during an external shock, one should wait till the device therapy is completed, in order not to interfere with it. Defibrillation patches should not be attached over transdermal medication patches and these should be removed before attaching the patches. If the person is lying in water, he should be moved out before using a defibrillator. But a person lying on snow or ice can be defibrillated. If the chest is drenched with water or perspiration, it should be wiped out before defibrillation pads are applied. Occasionally, unduly thick hair on the chest may require at least partial removal for successful defibrillation.