Hi, I'd like to help you with your question.
It is very common for people who have had heart surgery to experience a change in personalty or experience an increase in emotional difficulties. Heart surgery can cause psychological trauma so this may be why his behavior has changed. Anger, fear, irritability, lashing out and depression are all possibilities. It could be that the surgery interfered with your father's brain functioning, or it could be that having a serious illness that required heart surgery frightened your father and deepened his depression. He may also feel vulnerable as well.
However, that does not mean you or your mother need to allow him to become abusive. The fact that he is accusing your mother of having an affair and trying to restrict her activities and shoving her is abusive. If your father becomes physically violent, your mother may need to seek help either through the police or by leaving the home. She may need to stay away until he can get treatment. Here is a resource for your mother to help her find assistance:
If your father will not tell his doctor about these changes in personality, then you or your mother should. The doctor may not be able to share information with you about your father's case (unless you have a release signed), but you can certainly tell him/her what your father is acting like. That way, they can confront him the next time he goes for a checkup. The doctor can also prescribe medications to help your father with his depression and alleviate his symptoms.
The other possibility is that your father's medications are affecting him negatively. Side effects can have psychological impact so he may need a change in medicine to help him feel better.
Try talking with your father about this information and see if he would be willing to seek help. Talking about his experience would help him not feel so isolated and alone. He can talk with his doctor for a referral or he can search on line at http://therapists.psychologytoday.com/rms/.
There are also other resources that can help including, support groups. Here are some to get you started:
The Cardiac Recovery Handbook: The Complete Guide to Life After Heart Attack or Heart Surgery, Second Edition by Paul Kligfield
Coping With Heart Surgery and Bypassing Depression: A Family's Guide to the Medical, Emotional, and Practical Issues by Carol CoXXXXX, XXXXX Cohan MA and June B. Pimm Ph.D.
You can find these books on Amazon.com or your local library may have them for you.
I hope this has helped,