I just started in rad a few months ago and have only done a few heart ctas but this is what we do where I work:
#1 16g to RAC, sometimes 18g but we run contrast at up to 8, only @6 on 18g.
#2 we have either 2 med options: 15mg IV lopressor in 5mg doses. when we give this we give it like adenosine, hard and fast. we were lead so they are shooting while we are in there.
if that isn't working, we give 1/2 tab NTG SLG, as long as they don't take ED drugs.
The key for our pictures has been the 16g because they can run the contrast faster and get the images quicker.
We've also recently started hearts for valves and we don't give meds for that, just 16g.