Nonrebreathing valve at the distal end of a bag valve mask Nonrebreathing valve at the distal end of a bag valve mask. When the bag is squeezed to initiate positive-pressure ventilation, the flat disc section of the fishmouth valve is pushed onto its seat, and the fishmouth opens, allowing ventilation of patient through the fishmouth. Source: Bag Valve Mask and Mapleson Circuits, Anesthesia Equipment Simplified Citation: Rose G, McLarney J. Anesthesia Equipment Simplified; 2014 Available at: http://accessanesthesiology.mhmedical.com/DownloadImage.aspx?image=/data/books/871/rose001_fig_19-03.gif&sec=51861168&BookID=871&ChapterSecID=51860183&imagename= Accessed: November 05, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved