Yes good reply. I would just like to add that unnecessary risks are not taken. For example, if the blockage is large and in a tricky location, it is likely they will down tools and recommend you have bypass surgery. Most of the time though, the blockages are easily treatable and you will feel much better when the culprit blockage is opened up.
You are obviously awake during the procedure and if you feel very nervous, ask for some extra meds :) these are great at relaxing you.
risks of nitro are minimal...benefit of taking it is better blood flow to heart during angina. As for risks with Cath...you will be given form to sign...range will be little discomfort to damage to blood vessels or heart...basically though usually a well tolerated procedure and the long term benefits outweigh not doing it... all of this should have been discussed with you by doctors?see this web site.. http://www.nhlbi.nih.gov/health/dci/Diseases/cath/cath_risk.html