How often should the battery in a pacemaker be changed? how do you know if it's low?

Depends: Changing the batteries (actually, the entire device is replaced) depends on the settings you need to pace your heart. Approximately 5 years, however, it can be shorter or longer. There is an alarm that will sound if you've reached the threshold for replacement. Call your doc immediately if you should hear any unusual sounds...Also, you should have received a booklet explaing the features to you.

Usually 8-12 yrs: It depends on how old the pacemaker is (older devices have batteries with shorter lives) but generally, the current generation of devices last approximately 8 to 12 years. Your electrophysiologist can "interrogate" the device with a special computer to learn how much battery life is remaining.