Abstract: The lung inflation system specifically designed for use in the resuscitation of human beings. The system includes a manual compression bag which empties and refills through a single outlet opening. The compression bag is connected to a non-rebreathing valve which is specifically built, in accordance with the invention, so that the patient's lungs can be ventilated by means of the compression bag with pure oxygen, pure air, or a known mixture of both gases, as desired. The valve has a gas selector mechanism which makes it very easy for rescue personnel using the device to quickly select the mixture of gases which is needed. When available, oxygen from a pressurized oxygen source is supplied continuously to the valve device. The valve operates so that, when the compression bag is full, any excess oxygen being fed into the system is vented to the atmosphere through the same port as the one through which the breath exhaled by the patient passes.