Final answer:
The nurse should expect the heart rate to be fixed at 72 beats per minute regardless of activity.
Step-by-step explanation:
When a patient has a demand pacemaker inserted with the rate set at 72 beats per minute, the nurse should expect the heart rate to be fixed at 72 beats per minute regardless of activity. A demand pacemaker only activates and sends electrical impulses to the heart if the heart rate falls below the set rate. Therefore, the pacemaker will maintain the heart rate at the set rate even during activity.