locations of coronary arteries, drug-eluting stents?

Answer 1

Right and Left - coming off the main trunk of the aorta

the Left giving on a circumflex branch (which travels around the back of the heart) before continuing along down the anterior part of the heart as the Left Anterior Descending artery

Put the stents in the NARROW bit.

Answer 2

Here is a diagram of the coronary circulation:
http://mmserver.cjp.com/images/test/CoronariesFrontal.jpg

The stents are placed in areas that are narrowed, but have decent flow after the blockage:
http://content.answers.com/main/content/wp/en-commons/thumb/6/6b/250px-PTCA_stent_NIH.gif

Hope that helps.