Hi there ~
I understand your concerns. Yes, marijuana may have a lot of effects and your father's heart condition worsening may be attributed to his usage of the illegal substance. I believe that he needs to be seen by a psychiatrist. I suggest that you consult a psychiatrist
who is experienced in substance abuse
disorders so as to help him get off of his habit of using marijuana. I hope and wish your father a very quick and safe recovery.
I hope this helps. Take care and have a lovely day!