What must be done if the chest does not rise and fall during rescue breathing?

The correct course of action when the chest does not rise and fall during rescue breathing is to perform a head tilt/chin lift position. This technique is crucial because it helps open the airway by repositioning the victim's head, which may have been obstructed or not aligned properly. By tilting the head back and lifting the chin, it can create a clearer passage for air to enter the lungs, thus facilitating effective breaths.

Other options do not directly address the underlying issue of airway obstruction. Increasing the force of the breaths might lead to additional complications or even injury without ensuring that the airway is properly aligned. Changing the victim's head position could potentially resolve the issue, but the head tilt/chin lift is the most effective and recognized method to ensure an open airway. Waiting and trying again without adjusting the position can lead to ineffective efforts, prolonging the time the victim is without adequate oxygen.