I am a cardiology RN. I have seen many patients have an Implantable Cardiac Defibrillator. For most, it is a relatively simple procedure. There will be 2-3" incision under the left collar bone. The device is about the size of a half dollar. The doctor can decide whether your dad needs general anesthesia
(usually preferred) or just sedation. Your dad will be under certain activity restrictions for about 4-6 weeks. If the device fires, he will feel a shock
. Some people say it's pretty bad, while others say it's not as bad as they thought it would be. No matter what, if the device fires, he must report it to his doctor. Some patients do say they feel 'different' right before they get shocked. They are then able to sit down or pull off the road if they are driving.
If your dad's doctors have recommended this procedure, it is either because he is having life threatening arrythmias (irregular heart beats) or because his heart is not pumping as good as it should. In either case, this device will benefit greatly.
Best of luck to you and your dad.