The Ambu has a squeezable bag, a one-way valve, and a face mask. Compressing the bag opens a valve, forcing air through a mask or artificial airway into the lungs, according to the journal "Critical Care Nurse." Releasing the bag closes the valve and exhalation occurs passively through the exhalation port. During exhalation, the bag automatically refills with room air or oxygen. The cycle continues until spontaneous breathing occurs or breathing is mechanically supported by a breathing machine.

The ability to deliver increased amounts of oxygen via tubing and an oxygen tank improved the Ambu bag's versatility. The Ambu bag proved its merits in the field of emergency medical services and then moved to the hospital area. Placement and use in intensive care units, the emergency room, and general care units added to its value. The Ambu bag is also vital to the in-home care of patients dependent on breathing machines.