The invention concerns a nasal cannula assembly (10) adapted to deliver gases to a patient comprising a first compartment (1) and a second compartment (2) separated by a separation wall (6) a pair of nasal prongs (5) in fluid communication with the first compartment (1) the first compartment (1) comprising a first inlet (11) for introducing a first gas into said first compartment (1) the second compartment (2) comprising a second inlet (2) for introducing a second gas into said second compartment (2) and the separation wall (6) comprising at least one valve element (3) for controlling the passage of gas from the second compartment (2) to the first compartment (1). The invention concerns also a breathing assistance apparatus comprising a source of NO gas, and said nasal cannula assembly (10) in fluid communication with said source of NO gas.
