Sorry to hear about your Dad. As everyone is saying open heart surgery has almost become routine. It is amazing at what they can do now days.
I've been going through the medical woes with my folks and know how hard it can be on you. If you can go with your Dad to his appointments it would be a great help to him and you keeping things straight. I have been amazed at what my parents can not remember just hours after a doctor visit. As our parents get older it's like a role reversal happens. We become the care givers to them.
We'll keep your Dad and family in our prayers.