The invention concerns a breathing assistance apparatus having a source of Nitric Oxide in fluid communication with 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 flow restriction element (35) for controlling the passage of gas from the second compartment (2) to the first compartment (1).
