As mentioned above, a 45% lesion usually does not require either a stent or bypass. There mus be some more severe lesions than that. You should ask the exact severity and location of the lesions, and the reason fro the surgery: is it to alleviate symptoms of angina or congestive heart failure, or is it to prolong his life. And what are the risks and benefits from said approach.
No!!!!! 40% is nothing. 25% if the adult population is probably walking around with that. They like to give their young doctors practice on old people. He will probably survive the surgery and be a vegetable in a nursing home and die six months later. Get him out of that hospital.
I am not a Doctor, but I was told by a very good cardiologist that anything below 70% is not seen as a real threat. He told me also that a blockage up to and including around 50% should not normally give any symptoms because arteries are larger than they need to be, they can also expand considerably. For blockages of 40% I would seriously seek a second opinion.
Is it not also dangerous for someone to have such severe surgery having just had pneumonia?
If any traces of the infection are left in the lungs, this can become life threatening from major surgery because the body becomes weak. I think you are wise to investigate :)
I would also ask the specific reasons why the blockages cannot be stented, which is far less invasive and of course a far lower risk after pneumonia because only local anaesthetic is involved.