Pacemakers are generally checked at least every 3 months to allow plenty of time to change the generator when it is running low on power. Changing the generator simply means remaking the same incision, removing the old generator, and plugging the existing wires into the new generator. The patient goes home the same day. Most batteries last at least 5 years. Pacemakers sense every heart beat the patient has and only pace the heart when the patient's heart rate falls below a predetermined limit.
Patients are usually completely unaware of when the pacer is pacing their heart.
In some patients, the pacemaker only needs to fire very rarely because the slow heart beat only occurs intermittently. In other patients, the heart beat is always too slow and the pacemaker has to pace the heart all of the time. Such patients are said to be pacemaker dependent. Another use of pacemakers is for a disease called hypertrophic obstructive cardiomyopathy. This is a disease where overgrown heart muscle blocks the egress of blood out of the heart.