CPR masks and shields provide a protective barrier when first responders begin mouth-to-mouth resuscitation. They prevent the spread of contaminants between the patient and the first responder. CPR masks cover the patient's nose and mouth. First responders exhale into a one-way valve at the top of the mask to provide the patient with air. CPR shields have a flat, flexible surface and a one-way valve that first responders use to transfer air into the patient's mouth.