Abstract: A device for pulsed delivery of inhaled nitric oxide (NO) to a spontaneously breathing patient is disclosed. The device delivers NO, e.g., through a nasal cannula, only during the inspiratory phase of the breathing cycle. The device automatically executes a purge cycle when it is initially activated, and when the time between breath-triggered NO pulses reaches a predetermined time limit. The purge cycle protects the patient from exposure to NO.sub.2 that otherwise would accumulate in the fluid lines from the reaction of static NO with oxygen in the air.