What are the risk of having a heart disease byp operation?

i dont really know much about it but my uncle has just been diagnosed with cardiac disease or something along those lines, they thought he has angina but now hes been diagnosed with that. obviously i know any operation on the heart is dangerous but really what are the chances of him being ok, and how will he be after it. can anyone explain what exactly cardiac disease is and how you can prevent it from getting worse and stuff, i'd really like to know and i dont really want to ask my family because it will upset them. any help will be greatly appreciated. just any facts you have and stuff that will help me to understand it a little better, please dont post any websites as i have looked at loads and i dont really understand much of it very well unless you have one that would explain things in a way that is easy for me to understand. thanks so much