how can I help/support my dad? He is frightened of dying

[Gatekeeper]

my mam died two weeks ago and although they hadn't lived together for years or had a particularly good relationship it has hit him hard

He has had a cough for some time now and hasn't responded to anti biotics. After further tests at the GP his Doctor now thinks he may have heart failure and the cough plus his swollen ankles etc are a sign of this. He is now referred to a cardiologist and awaiting an appointment.

He is absolutely terrified and ringing up in a state of panic; I don't know what to do or say...he is 93 and prior to this was fit and active and looked/acted twenty years younger. I really don't know what to to say to him when he rings up; dh tactfully (NOT) says to me that he should be bloody grateful he came this far etc etc, which I get but it doesn't help me

He has always used me as his sounding board though and shared more info than I would like and Iend up anxious while he goes off whistling- feeling better for having 'vented'
Different this time though as he feels very mortal all of a sudden and doesn't like it