Multiple. Pacemaker ensure that the heart rate does not fall below a minimum programmed value. Dual chamber pacemakers restore the coordination (known as atrioventricular synchrony) between the upper and lower chambers of the heart. Pacemakers can also function in a limited capacity as monitors of heart rate, rhythm, and in some cases, estimate the degree of heart failure.
Prevent slow HR. Pacemakers prevent the heart from slowing too much. They are indicated for people with serious rhythm problems that cause the heart rate to fall below 50 BPM (in general). There are very specific guidelines that define when pacemakers are indicated.