The ventilator valve on demand for artificial ventilation of a patient is automatically adjusted on an open cycle to allow the arrival of selected volumes of oxygen at selected intervals. A pneumatic controller connected to a source of oxygen provides a control pressure for actuating the valve on demand, the cyclic adjustment being effected by pneumatic timers. The source of oxygen reaching the patient also passes through the regulator for energizing the valve in the request. A valve for regulating the flow volume and flow allows adjustment of flow when in an open position. In one embodiment, the valve to the application is composed of an assembly comprising a safety subassembly, in which is incorporated an indicating device displaying an overpressure condition in the assembly as a result of a judgment the arrival of oxygen to the patient and which also includes an anti-suffocation valve.