Judy, I have a history of diabetes, plus other heart issues, and fought the idea of a Pacemaker, which kenkeith and I believe you are referencing. I feel much better, my heart is much healthier since accepting a pacemaker, and am kicking myself for fighting it. I'm betting the doctor is trying to save your father's life. I'm also what is called a volunteer Navigator in the cardiac wing of a trauma hospital, and I see how much better people do after getting a pacemaker. Encourage your father to proceed with confidence, If the doctor is insisting, he must have good reason to do so. Keep us informed.
A low heart rate can cause fainting and a too heart rate can create irregular heartbeats. I assume it is a pacemakers that you reference. It is used to treat heart rhythms that are too slow, fast, or irregular. Pacemakers can relieve some symptoms related to irregular heartbeats. It can help your father who has an abnormal heart rhythm have some assurance of a stable heart rate.