Bad Tastes. Had Heart Attacks, Diabetic. Stent In Arteries, On Warfarin. Suggestions?

Hi, My Grandfather has recently been experiencing bad tastes in his mouth, and is not eating. He is 85 years old and has had a 3 heart attacks, the last one was just over a year ago. He is a type 2 diabetic, has had a stent put into one of his arteries to open up a blockage. His kidneys are also failing, but I am unsure of what medication he would be on. All I know is that he is taking Warfarin, and I have done some research and found that people who have stents put in often have after affects of metal tastes, although I believe he had that operation years ago. It seems his bad taste has started after his last heart attack, please help!