The KEMP USA 10-510 One Way Valve and Filter for CPR Masks is a single-use, one-way filter designed to be used in conjunction with compatible CPR masks (sold separately.) This valve contains a filter that protects the CPR giver while still allowing them to administer lifesaving "mouth to mouth" respiration efforts to the victim. Always use CPR equipment in accordance with manufacturer's instructions and adhere to best practices when administering first aid.