YR, I'm not surprised to hear about the heart rate. My father had the same thing happen after 5 bypasses and a valve replacement. His surgeon explained to him that this happens sometimes because the heart has been use to working extra hard from the blockages, etc. and it takes a while for it to get back into a "normal" beat. He didn't have to have the pacemaker put in, but his medications had to be adjusted and he stayed an extra 5 days before they allowed him to come home.
Your father will be okay. He's in good hands and the pacemaker may be what he needs. He's going to be sore for a while from the original surgery, but when he gets home, he's still going to have to take it easy.
I'm glad to hear that a nurse will be visiting them. This is a good step in the right direction. Prayers are being offered up each and every day from this home front.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.